Unit 5 Heredity Study Guide

Genotype: set of genes that an organism has

Phenotype: set of traits that an organism expresses

Dominant: a trait that appears in every generation (not every individual)

Recessive: sufficiently rare trait that skips every other generation (almost all affected individuals have non-affected parents)

Heterozygous: having two different alleles of a particular gene or genes

Homozygous: having two identical alleles of a particular gene or genes

True-breeding: where parents produce an offspring who carries the same phenotype

Hybrid: the offspring of two plants or animals of different species or varieties

Diploid: cells with 2 sets of chromosomes

Haploid: a cell contains a single set of chromosomes

Homologous chromosomes: a pair of chromosomes that are similar in size and shape and carry the same genes

Mitosis vs. Meiosis

Mitosis

Occurs in all organisms (except viruses)

Creates all body (somatic) cells

Involves one cell division

Produces 2 diploid daughter cells

Daughter cells are genetically identical

Creates a human cell with 46 chromosomes

Meiosis

Occurs only in fungi, animals, and fungi

Creates only sex (germ) cells

Involves 2 successive cell divisions

Produces 4 haploid daughter cells

Daughter cells are genetically different

Creates a human cell with 23 chromosomes

Both

Occurs in plants and animals

Starts with a diploid parent cell

Produces new cells

Cells undergo DNA replication

Same basic steps

Meiosis: Genetic Variation (how and when)

Crossing Over: in prophase I, the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes)

Random Fertilization: many different sperms paired up with many different egg cells which result in many diploid combinations

How do the movement of chromosomes during meiosis explain Mendel’s Law of Segregation of alleles and Mendel’s Law of Independent Assortment?

This law describes how the pair of alleles separate from one another during cellular meiosis division (gamete creation), leaving each gamete with only one allele. According to Mendel's law of independent assortment, genes sort independently of each other into gametes during meiosis. This occurs because chromosomes, on which the genes reside, assort independently during meiosis and crossovers cause most genes on the same chromosomes to also behave independently.

What is genetic linkage?

Refers to the closeness of genes or other DNA sequences to one another on the same sequence (map distance - units)

Practice Chi Square Problem

In mice, brown fur is dominant to white fur. A heterozygous brown mouse is mated to a white mouse. They produce 43 brown offspring and 47 white offspring. What is your null hypothesis? Are the observed numbers of offspring significantly different from the expected numbers? Why or why not? Show your work. (Brown Fur - B, White Fur - b)

H0: The amount of brown fur mice is equal to the amount of white fur mice. (No difference)

HA: There is more brown fur mice than the amount of white fur mice. (brown fur is dominant to white fur)

	B	b
b	Bb	bb
b	Bb	bb

	Observed	Expected
Brown Fur	43	45
White Fur	47	45
Total	90	90

DF: 1 x^2: .178 c-value: 3.841

Since the x^2 value of .178 is less than the c-value of 3.841, then we would fail to reject the null hypothesis and conclude that the amount of brown fur mice is equal to the amount of white fur mice, therefore, brown fur is not dominant than white fur.

How can environment affect phenotype?

Environment affects phenotype by ultimately affects the diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens. It can impact the way that an animal’s genes are expressed.

What is the difference between pleiotropy, epistasis, and genomic imprinting?

Pleiotropy: production by a single gene of two or more unrelated effects (occurs when a single gene determines multiple phenotypes)

Epistasis: the interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another (one gene affects the expression of another located at a different location)

Genomic Imprinting: the process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed

Karyotypes & Interpreting them

Male or Female Chromosomes? (XY or XX)

Females - 46 chromosomes, Males - 46 chromosomes

Aneuploid: one or more extra or missing chromosomes leading to an unbalanced chromosome complement, or any chromosome number that is not an exact multiple of the haploid number

Pedigree Review

Questions to ask:

Is the trait dominant (doesn’t skip generation) or recessive (skips generations)?

Is the trait autosomal (doesn’t matter about gender) or sex-linked (more affected males/females than affected females/males)?