Chapter 14 and 15 test review (Inheritance)

Name and discuss three sex-linked disorders.

1) Hemophilia is a rare bleeding disorder in which the blood doesn't clot normally. If you have hemophilia, you may bleed for a longer time than others after an injury. You also may bleed inside your body (internally), especially in your knees, ankles, and elbows. This bleeding can damage your organs and tissues and may be life threatening. 2) Muscular dystrophy is a group of genetic diseases in which muscle fibers are unusually susceptible to damage. These damaged muscles become progressively weaker. 3) Color blindness means that you have trouble seeing red, green, or blue or a mix of these colors.

What is meant by a dominant trait? How is a dominant trait symbolized?

A trait expressed preferentially over another trait. Symbolized by a capital letter. Ex) Y X T R

What is the law of independent assortment?

Alleles of different genes are assorted independently of one another during the formation of gametes

What is hybridization? What did Mendel call this generation?

Breeding two organisms with true-breeding traits. F1 generation.

Explain Mendel's role in the history of genetics.

Developed fundamental laws of heredity (law of independent assortment, law of segregation); experimented using pea plants; punnett square

Explain how independent assortment of alleles differs from segregation of alleles.

Every diploid cell has two alleles for every gene. Segregation means that when these alleles go through meiosis to create gametes, they will segregate from one another, and each of the haploid gametes will end up with only one allele. Independent assortment comes into play when you are looking at how the alleles of two genes separate. As long as each gene lies on a different chromosome, then the alleles of these genes will assort themselves independently of one another when the haploid gametes are formed in meiosis. Each haploid gamete can end up with a different combination of alleles of these two genes.

What are extranuclear genes? How are these genes inherited? Provide a human example of this inheritance and a disease that may result.

Genes included in the DNA present in organelles other than the nucleus, such as the mitochondria and chloroplasts, some of which code for the synthesis of proteins. The DNA of these organelles is inherited by the offspring via the cytoplasm of the gametes.

What are linked genes?

Genes that are inherited together because they are on the same chromosome.

What are true-breeding plants? What did Mendel call this generation?

Homozygous for the true-breeding trait. Parent generation.

Why are the terms homozygous and heterozygous meaningless in males when sex-linkage is involved?

Males only have one locus on their Y chromosome, making them hemizygous instead.

What is the F2 generation?

Offspring of a cross involving the F1 generation

What accounts for recombinants in linked genes?

Phenotypic ratio is 3:1. In contrast, linked genes, genes located on the same chromosome, tend to move together through meiosis and fertilization. Under normal Mendelian genetic rules, we would not expect linked genes to recombine into assortments of alleles not found in the parents. some mechanism must occasionally break the physical connection between genes on the same chromosome. This process, called crossing over, accounts for the recombination of linked genes.

What are recombinants?; what accounts for them in unlinked genes?

Recombination means that meiosis generates gametes with different allelic combinations than the original gametes the organism inherited; Recombination may be caused by loci on different chromosomes that sort independently or by a physical crossing over between two loci on the same chromosome, with breakage and exchange of strands of homologous chromosomes paired in meiotic prophase I. Phenotypic ratio is 9:3:3:1. The physical basis of recombination between unlinked genes is the random orientation of homologous chromosomes at metaphase I of meiosis, which leads to the independent assortment of alleles.

What is an allele?

The different forms of a gene. Y and y are different alleles of the gene that determines seed color. Alleles occupy the same locus, or position, on chromosomes

What determines recombination frequency?

The distance that the genes are away from each other on the chromosome. Genes that are adjacent have a recombination frequency near 0%, Genes that are very far apart on a chromosome have a recombination frequency of 50%, The relative distance between linked genes influences the amount of recombination observed

Explain who determines the sex of an offspring in humans.

The male does because he is the one that carries both the X and the Y chromosome. Whichever the baby receives will determine whether the baby is a girl (XX) or a boy (XY).

What is meant by a recessive trait? How is a recessive trait symbolized?

The opposite of dominant. A trait that is preferentially masked. Symbolized by a lowercase latter. Ex) y x t r

What is a barr body? What does it mean that "females consist of a mosaic of two types of cells"?

The small, dark-staining mass of inactive X chromosome within the nucleus of non-dividing cell. Although all their cells have the same two chromosomes, one from each parent, the mother's copy works in some cells, while the father's works in the others. The two kinds of cells often function differently, especially if one of chromosomes carries a defective gene. They have two types of cells in all their organs, each with one of the two X chromosomes genetically active and the other essentially silent. This allows adaptability, since each of the two X chromosomes carries different mutations and polymorphisms that can alter women's susceptibility or resistance to detrimental genes, infectious agents, or other environmental dangers.

If alleles do not sort independently of each other, what do we know about the location of the genes?

They are on the same chromosome.

What is genomic imprinting?

We all inherit two copies of every autosomal gene, one copy from our mother and one from our father. Both copies are functional for the majority of these genes; however, in a small subset one copy is turned off in a parent-of-origin dependent manner. These genes are called 'imprinted' because one copy of the gene was epigenetically marked or imprinted in either the egg or the sperm. Thus, the allelic expression of an imprinted gene depends upon whether it resided in a male or female the previous generation. Imprinted expression can also vary between tissues, developmental stages, and species

Explain the inheritance pattern when sex-linked genes are involved in inheritance.

X-linked recessive traits that are not related to feminine body characteristics are primarily expressed in the observable characteristics, or phenotype, of men. This is due to the fact that men only have one X chromosome. Subsequently, genes on that chromosome not coding for gender are usually expressed in the male phenotype even if they are recessive since there are no corresponding genes on the Y chromosome in most cases. In women, a recessive allele on one X chromosome is often masked in their phenotype by a dominant normal allele on the other. This explains why women are frequently carriers of X-linked traits but more rarely have them expressed in their own phenotypes.

Define: a) Character b) Trait

a) The sum of the relatively fixed personality traits and habitual modes of response of an individual. b) Characteristics or attributes of an organism that are expressed by genes and/or influenced by the environment

What were Mendel's outcomes for the following crosses?: a) Cross-pollinating true breeding purple flowered plants and true breeding white flowered plants. b) Self pollinating F1 purple flowered plants. What is the ratio of this outcome?

a) always has purple flowers b) 3:1 ratio of purple to white flowers

How did Mendel achieve a) self-pollination b)cross-pollination?

a) pollinated the plants himself to achieve true-breeding generation b) pollinated the plants himself while crossing the true-breeding generation to achieve hybrids

What is the chromosome theory of inheritance?

it is a basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns