Genetics

Kirsten Adams

National Cathedral School

AP Biology

Figure 14.0x Mendel

Figure 14.1 A genetic cross

Figure 14.2 Mendel tracked heritable characters for three generations

Figure 14.x1 Sweet pea flowers

Figure 14.3 Alleles, alternative versions of a gene

Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants

Figure 14.x2 Round and wrinkled peas

Figure 14.4 Mendel’s law of segregation (Layer 2)

Figure 14.5 Genotype versus phenotype

Figure 14.6 A testcross

Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross

Figure 14.8 Segregation of alleles and fertilization as chance events

Problem #1

• In garden peas, tallness is dominant and dwarfness is recessive. A heterozygous tall plant is crossed with a dwarf plant. If 40 offspring are produced, how many will be tall?

Problem #2

• In humans, brown eyes are dominant over blue eyes. A brown-eyed man and a blue-eyed woman have two blue-eyed children. What are the chances that their next child will have blue eyes?

Problem #3

• Cystic Fibrosis is inherited as a simple autosomal recessive. Suppose a woman who carries the trait marries a normal man who does not carry it. What percent of their children would be expected to have the disease?

Problem #4

• Classical Albinism is a single-gene disorder caused by the lack of an enzyme necessary for the synthesis of melanin pigments. Enzyme production requires the presence of one normal allele. What progeny and what proportions are expected from a normally pigmented woman who has an albino husband and an albino father?

Problem 5

• If two individuals with the genotype A/a B/b C/c D/d mate, what is the probabilty of getting an individual with the genotype A/A B/b c/c D/d?

Problem #6

• In watermelons, the genes for green color and for short shape are dominant over alleles for striped color and long shape. A plant that is heterozygous for green color and homozygous for short shape is crossed with a plant that is homozygous for striped color and heterosygous for short shape. What proportion of their offspring will be striped and short?

Incomplete Dominance and Codominance

Figure 14.9 Incomplete dominance in snapdragon color

Figure 14.9x Incomplete dominance in carnations

Problem #7

• In snap dragons, flower color and leaf color are both controlled by partial dominance. Pink flowers and light green leaves are the intermediate conditions. Supposed you crossed two plants, both of which had pink flowers and light green leaves. If there were 16 offspring, how many would you expect to have both pink flowers and light green leaves?

Multiple Alleles

Ex. Blood types

Figure 14.10 Multiple alleles for the ABO blood groups

Figure 14.10x ABO blood types

Problem 7

• A woman takes Mr. X to court for child support, but Mr. X swears he is not the father. The woman is blood type A and the baby is blood type A. Which blood type must Mr. X have to prove that he is not the father?

Interactions Between Genes

Pleiotropy

Epistasis

Collaboration

Complementation

Modifier Genes

Multiple Gene Inheritance

Pleiotropy

Figure 14.15 Pleiotropic effects of the sickle-cell allele in a homozygote

Epistasis

Figure 14.11 An example of epistasis

Collaboration

Problem 8

• If the dominant allele K is necessary for hearing, and the dominant allele M of another gene results in deafness no matter what other genes are present, what percentage of the offspring produced by the cross between k/k M/m and K/k m/m will be deaf?

Complementation

Modifier Genes

Multiple Gene Inheritance

Figure 14.12 A simplified model for polygenic inheritance of skin color

Environment

Penetrance

Expressivity

Figure 14.13 The effect of environment of phenotype

Sex linked characteristics

Holandric

X-linked

Figure 15.3 Sex-linked inheritance

Figure 15.9 The transmission of sex-linked recessive traits

Figure 15.10 X inactivation and the tortoiseshell cat

Figure 15.10x Calico cat

Pedigrees

Figure 14.14 Pedigree analysis

Figure 14.16 Large families provide excellent case studies of human genetics

Human Disorders

Figure 14.17 Testing a fetus for genetic disorders

Figure 15.0 Chromosomes

Figure 15.0x Chromosomes

Figure 15.11 Meiotic nondisjunction

Figure 15.12 A tetraploid mammal?

Figure 15.x1 Translocation

Figure 15.13 Alterations of chromosome structure

Figure 15.14 Down syndrome

Figure 15.x2 Klinefelter syndrome

Figure 15.x3 XYY karyotype

Linkage

Figure 15.4 Evidence for linked genes in Drosophila

Figure 15.5a Recombination due to crossing over

Figure 15.5b Recombination due to crossing over

Figure 15.6 Using recombination frequencies to construct a genetic map

Figure 15.7 A partial genetic map of a Drosophila chromosome

Linkage Problem

• In rabbits, a dominant gene produces spotted body color. Another dominant gene produces short hair and its recessive allele long hair. Rabbits heterozygous for both characteristics were mated with homozygous recessive rabbits. The results of this cross were as follows: 170 with spotted and short; 30 with solid and short hair; 26 with spotted and long; 174 with solid and long. What is the map distance between these genese?

Figure 15.15 Genomic imprinting (Layer 3)

Figure 15.16 Cytoplasmic inheritance in tomato leaves