Quarter 3 HSA Review Session

Genetics, Punnett Squares and Pedigrees

GENETICS

What is genetics?

The study of heredity, which is the passing of genetic traits from parents to offspring.

Genetics Vocabulary

Vocabulary Term Definition

Dominant

Recessive

Homozygous

Heterozygous

Genotype

Phenotype

The allele that is expressed

The allele that is hidden or masked when a dominant allele is present

When the 2 alleles of a particular gene in an individual are the same (ex: PP and pp)

When the 2 alleles of a particular gene in an individual are different (ex: Pp)

An organism’s genetic makeup; set of alleles (ex: PP, Pp, pp)

The physical appearance of a trait (ex: purple flowers or white flowers)

PUNNETT SQUARES

Punnett Square A punnett square is a tool that can used to predict the results of a

genetic cross

Can be used to predict the probability of passing on autosomal or sex-linked traits to offspring

Parent 2

Parent 1

One allele One allele

One allele

One allele

Autosomal vs. Sex-Linked Traits

The majority of traits that we inherit from our parents are not dependent on our sex → autosomal traits.

Genetic traits such as tongue rolling and having a widow’s peak will appear equally in both sexes.

However, certain traits are dependent upon one’s sex. They are determined by genes that are found on the sex chromosomes → sex-linked traits.

Example: Hemophilia (X-linked recessive disorder)

Autosomal Punnett Square Problem

Tall is dominant in pea plants, and short is recessive. T=tall and t=short. What are the genotypic and phenotypic ratios for a cross of a homozygous tall plant with a heterozygous tall plant?

Homozygous tall x Heterozygous tall

T T

T

t

TT

Tt

TT

Tt

Genotypic ratio- 1 TT : 1 Tt

Phenotypic ratio- 1 tall: 0

Sex-linked Punnett Square Problem

Hemophilia is an X-linked recessive disorder. A woman has hemophilia. She marries a man, who also has hemophilia. Write the genotypic and phenotypic ratios.

Xh Xh XhXh

XhY XhY

Xh Xh

Xh

Y

Genotypic ratio- 1 Xh Xh: 1 XhY

Phenotypic ratio- 1 female with hemophilia: 1 male with hemophilia

GENETICS AND PUNNETT SQUARE

QUESTIONS

Question 1

Which of these combinations results in the expression of a recessive trait?A.two dominant allelesB.a dominant sex-linked allele and a Y chromosomeC.two recessive allelesD.a dominant allele and a recessive allele

Question 2

Which of these is an example of a heterozygous genotype?A.RrB.RRC.wrinkledD.round

Question 3

In humans the trait of having freckles (F) is dominant to not having freckles (f).Which genotype and phenotype are correctly paired?A.FF—no frecklesB.Ff—no frecklesC.Ff—frecklesD.ff—freckles

Question 4

One kind of chromosomal mutation can occur during meiosis when a pair of chromosomes that carry genes for the same trait fail to separate. Which of these represents the sex chromosomes of a male organism when this type of chromosomal mutation has occurred? A.XXYB.XXC.XYD.XXX

Question 5

Red-green color blindness affects about 7.0% of the human male population. It affects approximately 0.4% of the human female population. These data suggest that red-green color blindness is aA.dominant trait carried on the Y chromosomeB.dominant trait carried on the X chromosomeC.recessive trait carried on the Y chromosomeD.recessive trait carried on the X chromosome

Question 6

In humans, the allele for dimples (D) is dominant. The allele for not having dimples (d) is recessive. A woman (DD) and a man (Dd) have four children. Which of these is the predicted ratio of the children with dimples to the children without dimples?A.1:0B.1:1C.1:3D.3:1

PEDIGREES

What is a pedigree?

A diagram that shows the occurrence of a genetic trait in several generations of a family

Indicates a Mating

Indicates offspring

Normal male

Normal Female

Affected Male

Carrier (Female)

Affected Female

Interpreting a Pedigree

1. Determine if the pedigree is autosomal or sex-linked

If the disorder occurs equally amongst men and women the disorder is autosomal.

If most of the males in the pedigree are affected by the disorder, it is sex-linked

Interpreting a Pedigree

2. Determine whether the disorder is dominant or recessive

If the disorder is dominant, only one parent of the affected child must have the disorder.

If the disorder is recessive, neither parent of the affected child has to have the disorder because they can be heterozygous.

The pedigree above traces the inheritance of dimples in a family.

1.Is the pedigree autosomal or sex-linked?

2.Is it dominant or recessive?

3.Label the genotypes of all of the individuals in the pedigree.

The pedigree above traces the inheritance of colorblindess in a family.

1.Is the pedigree autosomal or sex-linked?

2.Is it dominant or recessive?

3.Label the genotypes of all of the individuals in the pedigree.

PEDIGREE QUESTIONS

Question 7In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2.

Which of these individuals in the pedigree is a male with the genotype aa?A. Individual I-1B. Individual II-2C. Individual III-2D. Individual III-5

Question 8In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2.

Individuals III-6 and III-7 have two children and are expecting a third child. Their two children have flat feet. What is the chance that the third child will have normal arches?A.25%B.50%C.75%D.100%

Question 9In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2.

Which of these Punnett squares shows the cross between Individual II-4 and Individual II-5?