Chapter 15 Flashcards Preview

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Flashcards in Chapter 15 Deck (13):

Define the terms wild type and mutant.

• Wild type is normal phenotypes that are common in a population.
• Mutants are traits that are alternative to the wild type.


Are wild type phenotypes necessarily dominant phenotypes?

Wild type phenotypes are not necessarily dominant phenotypes.


Are mutant phenotypes necessarily recessive phenotypes?

Mutant phenotypes are necessarily recessive phenotypes.


What is the chromosome theory of inheritance?

The chromosome theory of inheritance states:
o Mendelian genes have specific loci (positions) on chromosomes.
o Chromosomes undergo segregation and independent assortment.


What is a sex-linked gene?

A gene that is located on either sex chromosome is called a sex-linked gene.


When are two genes said to be linked?

• Two genes are said to be linked when they are close together on the same chromosomes.


For a cross involving a sex-linked gene on the X chromosome in animals, predict 1) the ratio of males to females and 2) the genotypes and phenotypes of the offspring.

a. The male sperm determines the sex, 1:1 ratio in all organisms
b. For an X linked gene, the male shows a recessive phenotype because they only have ONE x chromosome


How can parents produce offspring with new combinations of phenotypes (1) with crossing over and (2) without crossing over?

• Crossing over rearranges the DNA sequence by crossing two different chromatids.
• Without crossing over, there is still random fertilization and independent assortment to help increase genetic diversity.


Why are males more affected by sex-linked traits than females?

males are hemizygous for the X chromosome. Females have two X chromosomes, whereas males only have one. This means that if a female has one normal allele and one affected allele, the trait will not be expressed (because it is recessive, the normal trait will be expressed instead). However, because males only have one X chromosome, if they have the affected trait, there is no normal trait on the other chromosome to cancel it out – so the trait will be expressed.


What is the definition of a syndrome?

A group of symptoms that consistently occur together or a condition characterized by a set of associated symptoms.


Compare and contrast aneuploidy and polyploidy.

• Aneuploidy refers to an abnormal number of a single chromosome. It results from the fertilization of gametes in which nondisjunction occurred. The offspring will either be short one chromosome, or have one chromosome too many.
• Polyploidy is a condition in which an organism has more than two complete sets of chromosome. Triploidy (3n) is three sets of chromosomes. Tetraploidy (4n) is four sets of chromosomes. Polyploids are more normal in appearance than aneuploids.


Which is more detrimental to an organism overall (aneuploidy or polyploidy)?

Aneuploidy is more detrimental to an organism overall.


What is a centimorgan?

A centimorgan is one map unit, which represents a 1% recombination frequency