Human Heredity

• There are 44 chromosomes that we call autosomal chromosomes.

• However, there are 2 chromosomes that determine our sex and we call them sex chromosomes.

• These 46 chromosomes all carry genes on them that determine our traits.

• Out of our 23 pairs of chromosomes, 1 pair is the sex chromosomes (X and Y).

• Female = XX

• Male = XY

Question?

If my parents have 5 boys in a row, what is the chance they will have a girl the next time?

50%

• Question: What is the probability that your parents will have a boy or girl?

• XY (dad) x XX (mom)

X Y

X

X

XX XY

XX XY

Phenotype:

50% boy

50% girl

Genotype:

50% XX

50% XY

Sex-linked gene:• Some traits are carried on the sex

chromosomes. Genes on the X or Y chromosomes are sex-linked genes.

• These traits are passed on from parent to child. Sex- linked genes can be recessive or dominant.

• MALES are more likely to have a sex-linked trait because they only have ONE X and Y. The allele is USUALLY on the X chromosome.

• Ex. colorblindness, hemophilia, hairy ears, muscular dystrophy

Carrier – person who has one recessive allele and one dominant allele for a trait or heterozygous for that trait (only women can be carriers).

Example

Hemophiliac carrier XHXh

Colorblind carrier XBXb

Sex linked Punnett Squares:Question: What is the probability that a carrier female and a

colorblind male will have a girl who is colorblind (b = colorblind, B = normal)?

YXb

XB

Xb

XBXb

XbXb XbY

XBY

Phenotype:

25% normal boy

25% colorblind boy

25% normal girl

25% colorblind girl

Try this one on your own

Question:

What is the probability that a homozygous (normal vision) female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)?

XB

XB

XBXb

XBXb XBY

XBY

Xb YPhenotype:

50% normal girls

50% normal boys

Parents: XBXB x XbY

Genetics Disorders and Mutations

Mutations …

• are changes in the genetic material

• can be good or bad• can be on a single

gene or the whole chromosome

Genetic Disorder – abnormal condition that a person inherits

through genes or chromosomes.

They are caused by mutations or changes in a person’s DNA.

Write down 3 disorders that have affected someone you know.

Cystic Fibrosis• Genetic disorder where the body produces abnormally thick mucus

in the lungs and intestines making respiration and digestion difficult• caused by a mutation in a gene. The product of this gene is a

chloride ion channel important in creating sweat, digestive juices and mucus.

• One in four babies are born with cystic fibrosis• Most common among Northern European descent

Sickle Cell Anemia• Sickle cell is a genetic disorder that affects the

blood’s hemoglobin. Hemoglobin is the protein in your blood that carries oxygen.

• Sickle-cell anemia is caused by a point mutation in protein chain of hemoglobin, replacing the amino acid glutamic acid with the amino acid valine

• The ‘sickle shape’ of the cell doesn’t allow the red blood cell to carry very much oxygen.

• Most common among African American descent

Famous People with Sickle Cell DiseaseMiles Davis, jazz musician.

Paul Williams, singer (The Temptations) Georgeanna Tillman, singer (The Marvelettes)

Tionne "T-Boz" Watkins, singer (TLC)

Hemophilia• Hemophilia is a genetic disorder in which a person’s

blood clots VERY slowly or not at all. • A person with hemophilia can bleed to death from a

paper cut or scrape. • This is sex-linked disorder on the X chromosome.

– Queen Elizabeth suffered from this disorder.

This man received a vaccine. This is what having hemophilia did to is body.

Down Syndrome• Down Syndrome is a genetic disorder that

occurs when an individual receives an extra copy of a chromosome.

• A mistake occurs during Meiosis I: the chromosomes failed to separate correctly (non-disjunction) therefore leaving an extra copy of chromosome #21.

• Doctor’s use tools like amniocentesis and karyotypes to help detect most diseases.

What is a karyotype?

• Picture of your chromosomes

• Arranged from largest to smallest

• quickly identify chromosomal changes

Sex-linked-Practice on your own:

• What is the probability of a female carrier of hemophilia and a normal male having a boy with hemophilia?

• What is the probability of a man with hairy ears and a normal female (not a carrier) having a child with hairy ears?

• What is the probability of a carrier woman and a male with muscular dystrophy having a girl with muscular dystrophy?