human genetics. how many pairs of chromosomes are in each of our body cells? a.32 b.23 c.46 d.16 23...

44
Human Genetics

Upload: marvin-barrett

Post on 21-Jan-2016

219 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Human Genetics

Page 2: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

How many pairs of chromosomes are in each of our body cells?

A. 32B. 23C. 46D. 16

23 pairs! This is 46 total; we get 23 from mom & 23 from dad.

Page 3: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Body cells are also known as what?

A. GametesB. HistonesC. ChromatinD. Somatic Cells

Somatic Cells!

Page 4: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Which cells in our bodies do NOT have all 46 chromosomes?

A. GametesB. HistonesC. ChromatinD. Somatic Cells

Gametes! Gametes are also known as sex cells. THESE ARE SPERM & EGG CELLS!

Page 5: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

How many chromosomes do human sperm or egg cells contain?

A. 32B. 23C. 46D. 16

23! They do NOT get 2 copies of each chromosome; they just get 1!

Page 6: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Gametes – Sperm & Egg Cells

• All gametes are haploid.

• In humans, that means each egg cell & each sperm cell has 1 copy of each chromosome (23 total chromosomes).– Egg Cells: all human egg cells carry 23 chromosomes, 1 of

which is a single X chromosome– Sperm Cells: in males, there are 2 types of sperm cells – 1

carries an X chromosome & 1 carries a Y chromosome

Page 7: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

The 2 Types of Chromosomes

• Autosomes: non-sex chromosomes– Of the 46 chromosomes, 44 of them (22 pairs) are

autosomes.

• Sex Chromosomes: the last 2 chromosomes; they determine the sex of the person– Females have 2 X chromosomes (XX).– Males have 1 X and 1 Y chromosome (XY).

Is this person male or female?

Page 8: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

When a sperm & egg cell combine, half the time the fertilized eggs (zygotes) are female & half of the time

they’re male.

Page 9: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

FUN FACT!

There are actually slightly more men on Earth than women.

WHY? Shouldn’t it be half & half?

Since the Y chromosome is so much smaller, it’s lighter. That means that

the sperm cells that carry the Y chromosome can swim a little faster! This gives them an advantage & they can reach the egg cell more quickly!

Page 10: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Karyotypes – what’s that?

Page 11: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Karyotypes

• Scientists can analyze an individual’s chromosomes by taking a picture of cells during mitosis.

Why does this need to be done during mitosis?

• It’s easiest to view chromosomes during mitosis, because they are condensed!

Page 12: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Karyotypes

• From a picture of chromosomes, scientists can cut & paste to arrange the chromosomes in pairs to form a karyotype.

The last pair (#23) is the sex chromosomes.

Page 14: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

A. Man B. Woman

Man!It’s not labeled, but you can see that 1 of the sex chromosomes

is much smaller than the other (the X & the Y).

Page 15: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Why is karyotyping important?

Page 16: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Using Karyotypes• Genetic disorders can be identified by looking at an

individual’s karyotype.

Down Syndrome can be confirmed even before the baby is

born!

Page 17: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Human Chromosome Disorders

How often do they occur?

• Relatively high frequency in humans, but most embryos are spontaneously aborted– Developmental problems result from biochemical

imbalances.

About 60% of first trimester miscarriages are due to chromosome disorders.

Between 5-10% of stillborn deliveries are due to

chromosome disorders.

Page 18: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Human Chromosome Disorders

• Some conditions are survivable.

How do chromosome disorders occur?

Page 19: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Chromosome Abnormalities

• Incorrect number of chromosomes/mutations within the chromosome– Nondisjunction: chromosomes don’t separate properly

during meiosis– Chromosome Mutations: deletion, inversion, duplication,

translocation

Page 20: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Remember!

• During meiosis, a diploid cell (2 copies of each chromosome) divides & produces 4 haploid gametes (sperm or egg).– Gametes only have 1 copy of each chromosome!

Page 21: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Nondisjunction

• Sometimes, chromosomes may not separate properly during meiosis; this is called nondisjunction.

• If nondisjunction occurs, abnormal numbers of chromosomes (1 extra or 1 missing) are found in gametes & chromosomal disorders may result.

Page 22: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Nondisjunction

• Homologous chromosomes don’t separate properly during Meiosis 1.

OR

• Sister chromatids fail to separate during Meiosis 2.

Page 23: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from
Page 24: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Nondisjunction

• Trisomy: cells have 3 copies of a chromosome– In trisomies, the gamete

of one parent donated 2 of one type of chromosome to the child & the gamete of the other parent donated 1 (like normal).

Page 25: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Nondisjunction

• Monosomy: missing 1 chromosome– In monosomies, the gamete of one parent donated 1

chromosome & the other parent did not donate any.

Page 26: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Down Syndrome• Trisomy 21

– Every 1 in 700 children born in the US have Trisomy 21.

Chromosome 21 is the smallest, but an

abnormality still has severe effects.

Page 27: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Down Syndrome vs. Age of Mother

Mother’s ageIncidence of Down

Syndrome

Under 30 <1 in 1000

30 1 in 900

35 1 in 400

36 1 in 300

37 1 in 230

38 1 in 180

39 1 in 135

40 1 in 105

42 1 in 60

44 1 in 35

46 1 in 20

48 1 in 16

49 1 in 12

Women are born with all the egg cells they’ll ever have.

So, a 35 year old woman has 35 year old egg cells.

Page 28: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Other Examples of Disorders caused by Nondisjunction

• Klinefelter’s Syndrome – XXY (male)• Turner’s Syndrome – XO (female)

As long as there’s at least 1 Y chromosome, the karyotype is male!

Page 29: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Klinefelter’s Syndrome

• XXY– 1/2000 live births– Have male sex organs, but

are sterile– Feminine characteristics

• Some breast development

• Lack of facial hair– Tall– Normal intelligence

Page 30: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Turner’s Syndrome

• XO (1 X chromosome)– 1/5000 births– Varied degrees of effects– Webbed neck– Short stature– Sterile

Page 31: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Jacob’s Syndrome

• XYY– 1/1000 live births– Extra Y chromosome– Slightly taller than average– More active– Normal intelligence, slight

learning disabilities– Delayed emotional maturity– Normal sexual development Some men will never know

they have Jacob’s Syndrome!

Page 32: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Trisomy X

• XXX– 1/2000 live births– Produces healthy females!

• All but 1 X chromosome are inactivated.

Most mammals leave only 1 X chromosome activated in their cells. The inactivated chromosome(s) are

called barr bodies!

Page 33: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Remember! Chromosomal Mutations

• Error in replication:– Deletion: loss of a

chromosomal segment– Duplication: repeat a

segment

• Error in crossing over:– Inversion: reverses a

segment– Translocation: move

segment from 1 chromosome to another

Page 34: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

How do we know if a growing embryo has a chromosome abnormality?

Genetic Testing!• Amniocentesis: a syringe takes a sample of the embryo cells,

then stains & photographs the chromosomes– Analysis of the karyotype

Page 35: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

The Human Genome Project

• The genome of many organisms has been determined, including the human genome!

• Now, we are analyzing the code, finding genes coding for different traits, & discovering ways to isolate them & manipulate them.

• In gene therapy, an absent gene or faulty gene is replaced by a normal, working gene!

Video – Blind Dog Gene Therapy

Page 36: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Pedigrees – what are those?

Page 37: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Pedigrees

• Similar to a family tree; both are used to show relationships in a family

• Used to demonstrate how traits are passed from 1 generation to another

• Genetic counselors use pedigrees to follow how genetic disorders are inherited.

Page 38: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Pedigrees

• People who are heterozygous for a recessive genetic disorder (they are unaffected) are called carriers.– Sometimes, carriers of traits may be represented as a half-

shaded shape or a shape with a dot in the middle.

Page 39: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Pedigree Symbols

• Square: male• Circle: female• Shaded: affected individual

• Open: unaffected• Horizontal Line: marriage• Vertical Line & Bracket:

descendants of a marriage

Page 40: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

female male

marriage parents children

Page 41: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Most genetic disorders are caused by mutations on autosomes (non-sex chromosomes).

• Autosomal Recessive Disorders: albinism, cystic fibrosis, tay-sachs disease

• Autosomal Dominant Disorders: achondroplasia (common form of dwarfism)

• Codominant Disorders

Page 42: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

• Could this trait be inherited as a simple autosomal recessive?• Could this trait be inherited as a simple autosomal dominant?• Could this trait be inherited as a simple X-linked recessive?• Could this trait be inherited as a simple X-linked dominant?• Could this trait be inherited as a simple Y-linked trait?

Page 43: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

• Could this trait be inherited as a simple autosomal recessive?• Could this trait be inherited as a simple autosomal dominant?• Could this trait be inherited as a simple X-linked recessive?• Could this trait be inherited as a simple X-linked dominant?• Could this trait be inherited as a simple Y-linked trait?

Page 44: Human Genetics. How many pairs of chromosomes are in each of our body cells? A.32 B.23 C.46 D.16 23 pairs! This is 46 total; we get 23 from mom & 23 from

Draw the Pedigree!

• An unaffected man marries a woman who is a carrier for Duchenne Muscular Dystrophy, which is attributed to an X-linked gene.

• They have 4 children, 1 son with Duchenne, 1 carrier daughter and a daughter & son who are unaffected.

• The child with Duchenne Muscular Dystrophy dies in childhood.

• The carrier daughter marries and has 3 children of her own, 2 of which are carriers and 1 daughter of which is unaffected.