THE PASSING OF TRAITS FROM PARENT TO OFFSPRING

“Looking at Your Traits”

• Number your paper 1-10

• Beside each number, write the “Trait” we are looking at.

• Tell whether you are “dominant” or “recessive” for this trait.

• Lastly, write your “Genotype”—which will be represented by given letters

Ex.1. PTC-Dominant-TT or Tt

2. Tongue Rolling-Dominant-RR or Rr

“Looking at Your Traits”

1. PTC is a chemical called phenylthio-carbamide and is harmless. It is used in medical genetics and as a diagnostic tool in medicine. The ability to taste the chemical is a dominant trait. People who cannot taste this chemical are recessive for the trait.

“Looking at Your Traits”

2. Tongue Rolling

“Looking at Your Traits”

3. Earlobes

“Looking at Your Traits”

4. Earbump

“Looking at Your Traits”

5. Widow’s Peak

“Looking at Your Traits”

6. Hitchhiker’s Thumb

“Looking at Your Traits”

7. Polydactyly

“Looking at Your Traits”

8. Syndactyly

“Looking at Your Traits”

9. Cleft Chin

“Looking at Your Traits”

10. Hair Whorl

I. Terms

• Trait – characteristic of an organism• Gene – a heredity unit that codes for a trait.• Allele – different gene forms• Dominant – the gene that is expressed

whenever it is present• Recessive – the gene that is “hidden”. It is

not expressed unless a homozygous condition exists for the gene.

I. Terms

• Homozygous – two identical (same) alleles for a given trait (TT).

• Heterozygous – two different (opposite) alleles for a given trait (Tt).

• Gamete – sexual reproductive cell.• Fertilization – the fusion of two gametes.• Phenotype – physical trait of an organism.• Genotype – the genes present in the cell.

II. Gregor Mendel-“The Father of Genetics”

A.*Mendel was the first to come up with rules regarding heredity-which formed the basis of genetics.

B. Mendel’s Hypotheses

1. For each inherited trait, an individual has two factors that control heredity (these “factors” are called genes) which are inherited from each parent.

B. Mendel’s Hypotheses

2. There are alternative versions of genes—(each version is called an allele).

Ex. Purple flowers or white flowers

Brown eyes or blue eyes

B. Mendel’s Hypotheses

3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance.

--Dominant or recessive Purple flowers are dominant to white flowers

B. Mendel’s Hypotheses

4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited trait. When gametes unite during fertilization, each gamete contributes one allele.

C. Laws of Heredity

1. Law of Segregation—the two alleles for a trait segregate (separate) during the formation of gametes (meiosis).

2. Law of Independent Assortment—the alleles of different genes separate independently of one another during gamete formation.

*Ex. The alleles for height separate independently of the alleles for flower color

III. Studying Heredity

A. Punnett Square

1. Determine the traits used.

2. Determine the dominant vs. recessive trait.

3. Determine the letters for each trait.

4. Express the cross and determine the gametes formed.

5. Set up Punnett Square.

Punnett Square

• Place the two female gametes across the top• Place the two male gametes down the side.• Determine the offspring by filling in the squares.

Ex. Problem

• Trait-Eye Color• Brown is dominant to

blue• B = Brown

b = blue

* Cross a homozygous brown eyed male with a blue eyed female.

BB bbx

B

B

b b

b

bb

bB

B B

B

Genotypic ratio: ___:___:___

Phenotypic ratio:____:____

0 04

4 0

Passing on of Traits

IV. Sexual Reproduction-reproduction where two gametes

unite.

--Two parents each form reproductive cells that have one-half the number of chromosomes—these cells are called gametes and the process that they are

made is called meiosis.

Sexual Reproduction

A. MEIOSIS--A form of cell division

that halves the number of chromosomes when forming specialized reproductive cells, such as gametes.

**Four cells are produced, each with half as much genetic material as the

original cell.

B. Chromosome Number in a Cell

1.Diploid number 2n—the number of chromosomes in a body cell of an organism.

2.Haploid number n—half of the diploid number.– The diploid number for a human is 46 (humans

have 46 chromosomes in each body cell)– The haploid number for a human is ___ and is

found only in the gamete cells (sperm/egg)23

2n n Homo sapiens (human) 46 23

Mus musculus (house mouse) 40 ___

Zea mays (corn or maize) 20 ___

Drosophila melanogaster (fruit fly) ___ 4

Xenopus laevis (South African clawed frog) ___ 18

Caenorhabditis elegans (microscopic roundworm) ___ 6

Saccharomyces cerevisiae (budding yeast) 32 ___

Canis familiaris (domestic dog) 78 ___

Arabidopsis thaliana (plant in the mustard family) 10 ___

Muntiacus muntjac (its Indian cousin) ___ 3

Myrmecia pilosula (an ant) ___ 1

Parascaris equorum var. univalens (parasitic roundworm) 2 ___

Cambarus clarkii (a crayfish) 200 ___

Equisetum arvense (field horsetail, a plant) 216 ___

Determine the Diploid or Haploid number of each organism:

20

10

8

36

12

16

39

5

6

2

1

100

108

Meiosis and Sexual Reproduction

Question:What is the difference in the number of cell divisions and the change in chromosome number during mitosis and meiosis?

Meiosis and Sexual Reproduction

MeiosisMitosis

2n

n2n 2n

2n

n

n n n n

C. Mitosis VS. Meiosis

Mitosis• Produce identical cells• Produce diploid cells• Occurs in:

– Plants—stems, leaves, roots

– Animals—skin, bones, digestive organs, etc.

Meiosis• Produce gametes (sex

cells)• Produce haploid cells• Occurs in:

– Plants—ovules, spores

– Animals—ovules (eggs), sperm

V. Genetic Problems

Genetic Diseases

• http://www.marchofdimes.com/pnhec/4439_4136.asp

A. Pedigrees• Pedigree help determine the inheritance and

probability of human genetic disorders.

Generation:

Generation:

Generation:

Generation:

Example Pedigree

B. Karyotype--A picture of the paired chromosomes,

arranged in order from largest to smallest.In humans, there are 23 pairs of chromosomes.-22 autosomes (chromosomes that code for regular body traits)

-1 sex chromosome

Gender is determined by the combination of sex chromosomes inherited in the zygote (the fertilized egg).

XX = Female

XY = Male

*it is the sex chromosome with in the sperm that is the determining factor for gender.

Karyotypes

• Karyotypes can be obtained by blood samples or by amniocentisis.

• Amniocentesis detects or rules out Down's syndrome. Amniocentesis also detects neural tube defects such as spina bifida. Babies born with spina bifida have a backbone that did not close properly. Serious complications of spina bifida can include leg paralysis, bladder and kidney defects, brain swelling (hydrocephalus), and mental retardation. If a pregnancy is complicated by a condition such as rh-incompatibility, your doctor can use amniocentesis to find out if your baby's lungs are developed enough to endure an early delivery.

Amniocentesis

C. Nondisjunction- the failure of chromosomes to separate properly

during meiosis.

• Karyotypes can also detect other chromosomal abnormalities such as:– Down’s Syndrome—an extra #21 autosome.– Klinefelter’s Syndrome—an extra sex

chromosome– Turner’s Syndrome—a missing sex

chromosome