Mastering Biology 5

Why are linked genes inherited as a set rather than independently?

Linked genes are located near each other on the same chromosomes, so they tend to move together.

Fur color in rabbits is controlled by multiple alleles. What does this mean?

Rabbit fur color is controlled by a single gene, but there are multiple versions of that gene.

__________ are linked together at the centromere.

Sister chromatids

This karyotype corresponds to which of the following individuals?

a female with Down Syndrome

If you are a male, the Law of Independent Assortment indicates that your gametes contain _____.

a random mix of the chromosomes you inherited from each parent

What is a carrier?

an individual who is heterozygous for a particular recessive trait

Imagine that, in cats, eye color is controlled by a single gene and that black eyes are dominant to orange eyes. All the offspring of a cross between a black-eyed cat and an orange-eyed cat have black eyes. This means that the allele for black eyes is __________ the allele for orange eyes.

dominant to

Crossing over happens during __________.

meiosis

In animals, meiosis __________.

produces four gamete cells

How have Mendel's laws fared as we have learned more about cell biology and processes such as meiosis?

Our new knowledge has helped to explain some of the exceptions to Mendel's laws of inheritance.

The inheritance pattern for red-green color blindness is different for males compared to females. Similar to the inheritance pattern for hemophilia in the royal families of Europe, red-green color blindness is rare in females although they can be carriers for this trait. Why is the inheritance pattern different for males and females?

The gene for this trait is located on the X chromosome.

If it were to be stretched out, the DNA in one of your cells would be taller than you. How does such a large quantity of DNA fit within the nucleus of one of your cells?

DNA is associated with proteins that compact the DNA to form a package called chromatin.

A breeder wants to set up a program to produce zebrafish with long fins. Having long fins is a dominant trait compared to the short fin wild type. Before she can market her zebrafish, she needs to perform a test cross on the long-finned fish she plans to use as a breeder. How can she tell whether her fish are homozygous or heterozygous for the long-finned trait?

Do several test crosses between the long-finned fish and the short-finned fish; if the offspring are always long finned, the long-finned parent is probably homozygous.

What do we call a genetic cross that follows two separate characters, such as pea seed color and pea seed shape?

a dihybrid cross

Duplication of the chromosomes by a cell occurs __________.

before a cell divides

Mendel's Law of Independent Assortment states that __________.

each pair of alleles segregates independently of the other pairs of alleles

Consider the image. It shows a cell undergoing cytokinesis. You can determine this is a plant cell rather than an animal cell because it has __________.

formed a cell plate

Mendel observed that pairs of alleles were separated or segregated in gametes and that they were rejoined in fertilization. We know that pairs of _____ are segregated in _____ and then are rejoined through fertilization.

homologous chromosomes ... meiosis

Random orientation of homologous pairs of chromosomes during meiosis I results in alternative arrangements that contribute to genetic variation in offspring. This is called __________.

independent assortment

After fertilization, the resulting zygote undergoes _____.

mitosis

Mendel formulated his principles of inheritance based on _____.

observations on the outcomes of breeding experiments. The underlying processes were unknown at the time.

Except during __________, cell division in humans results in daughter cells that have the same number of chromosomes and are genetically identical to each other and to the parent cell.

sexual reproduction

As we now understand it, the Law of Independent Assortment applies _____.

to pairs of genes that are on different chromosomes, but NOT to pairs of genes that are close together on the same chromosome

Like mitosis, meiosis involves duplication of the chromosomes before division starts. However, there are __________ rounds of cell division during meiosis and __________ during mitosis.

two; one