Genetics Lab Exam

Meiosis.

Chromosome diagram.

What is genetics?

The study of how traits are passed on from one generation to the next.

What are Gregor Mendel’s three basic principles? (two of which are now laws)

Principle of Dominance - when parents differ in one characteristic, their hybrid offspring resemble only one of the parents and are not a blend of the two parent phenotypes.

Mendel’s First Law (aka - Principle of Segregation) - alleles of one gene segregate from one another during the formation of gametes.

Mendel’s Second Law - alleles of different genes sort independently of one another during gamete formation. (one trait does not influence the inheritance of another trait)

Initially described using pea plants.

What is genotype?

The genetic makeup of an organism.

What is phenotype?

The physical characteristics of an organism that are the result of its expressed genes.

Indicated using descriptive words.

What is frequency?

The proportion of one type of individual to the total population.

Always between 0 and 1, and will add up to 1.

What is a ratio?

The proportion of one thing to another.

What is homozygous?

The same gene alleles.

An individual with two identical alleles for the same gene.

What is heterozygous?

Different gene alleles.

An individual with two different alleles for the same gene.

Punnet Squares

A diagram commonly used for predicting the outcome of simple genetic crosses.

Used to simulate all possible combinations of gametes.

• monohybrid cross - a cross between two individuals that differ in respect to one characteristic.

• dihybrid cross - experimental mating between two individuals that differ with respect to two characteristics. Must use the FOIL technique in order to create gamete combinations. The duplicates can be ignored and only expressed once.

• test cross → determine if the genes are linked at the same chromosome. Mating between an individual of unknown genotype for a particular characteristic and an individual that is homozygous recessive for that characteristic.

What is a gene?

A unit of hereditary information that contributes to the inherited characteristics of an organism, composed of a specific organized sequence of DNA.

Specific nucleotide sequences at particular locations on chromosomes that act as factors of inheritance for a particular trait or characteristic.

What is an allele?

Alternative version of a gene, either dominant or recessive.

Slight variations in the gene sequence that change the resulting proteins.

What is dominant?

An allele that is expressed in both heterozygous and homozygous conditions.

Represented by uppercase letters.

What is recessive?

An allele that is not expressed phenotypically in heterozygous conditions.

Represented by lowercase letters.

What is independent assortment?

Mendel’s Second Law.

The phenotype ends up being a 9:3:3:1 ratio.

What is gene linkage?

Genes that are located close together on the same chromosome and are inherited together. (less than 50 map units apart)

Where do our genes come from?

Your parents, as a result of fusion of their gametes.

In order to produce offspring, both parents must go through meiosis to create haploid gametes, which fuse during fertilization to make the next generation.

What are chromosomes made of?

DNA, which is a collection of genes.

What is diploid?

Meaning two copies.

What is haploid?

Meaning only one copy of each.

Product of meiosis.

What is crossing over?

The exchange of segments of the non-sister chromatids of homologous chromosomes when they are in tetras during prophase I of meiosis.

What is a tetrad?

A paired set of homologous chromosomes, each made up of two sister chromatids, closely associated at the centromeres, formed during prophase I of meiosis.

bivalent - a pair of homologous chromosomes.

What are recombinant gametes?

Gametes that are a result of crossing over or recombination between parental gametes.

Combinations that are produced despite gene linkage.

These are less frequently produced combinations.

What determines the chance of having a breakage and recombination event between a given pair of genes?

Depends upon how far apart they are on the chromosome.

The farther apart the genes, the greater the chance of a breakage occurring between the two genes. This would result in a relatively large number of recombinant gametes produced during meiosis.

If the two genes are close together, there are relatively few breakages between them, consequently a relatively low number of recombinant gametes.

How to solve genetics problems.

1. write down all the information given in the problem

• which allele is dominant

• which allele is recessive

• what are the genotypes of all the individuals involved

2. determine the gametes by all individuals

3. draw a punnet square to predict the offspring of the cross described

4. answer the question as asked

What are sex chromosomes?

A distinctive pair of chromosomes that are different in males and females.

The morphology of a single pair of sex chromosomes determines whether an individual is male or female.

What are autosomes?

The non-sex chromosomes in the nucleus. (in humans, there are 22 pairs)

Autosomal genes - the inheritance genes that are found on autosomes.

What is a karyotype?

The photographic representation of the chromosomes of an actively dividing cell, showing the number, shape, and size of the chromosomes.

Turner syndrome.

When there is only one sex chromosome present instead of two.

Some phenotypic characteristics may include:

• short stature

• webbed neck

• broad chest

• infertility

• cardiovascular problems

• possible learning difficulties

Down syndrome. (trisomy 21)

There are three chromosomes on the 21st pair instead of two.

Some phenotypic characteristics may include:

• intellectual disability

• distinctive facial features

• low muscle tone

• short stature

• heart defects

• increased infection risk

Klinefelter syndrome.

There are two X chromosomes and one Y chromosome instead of one of each like in the normal male.

Some phenotypic characteristics may include:

• infertility

• tall stature

• gynecomastia

• less body hair

• potential learning difficulties

What is sex linkage?

The gene found on the sex chromosomes, typically referring to genes found on the X but not the Y chromosome in humans.

Genes located on the X chromosome.

What is a pedigree chart?

A diagram that shows the occurrence of phenotypic traits or genetic diseases in successive generations, usually in humans, enabling the analysis of how these traits are passed from the parents to the offspring.

What is one challenge in the analysis of pedigree charts?

Identifying the type of inheritance for a trait.

(autosomal or sex-linked, dominant or recessive alleles)

What is a carrier?

Refers to an individual who has the recessive allele for a condition or disease but does not express any symptoms of the condition or disease. (the individual would be heterozygous for the trait)

Males cannot be carriers since they only have one X chromosome.

This would mean a “carrier” is a heterozygous female.

What is polygenic inheritance?

Phenotypic traits that involve contributions from the alleles of several or many genes at multiple locations on the chromosome, typically with an additive effect.

Polygenic traits show a continuous range of phenotypes in a population that approximates a normal distribution.

• height

• skin pigment

• IQ

• total yield of crop varieties

• production levels of milk in cattle

Class example: make a hypothetical assumption that five different genes contribute to hand span in humans.

What is normal distribution?

A set of continuous data for which the mean is the most common value, with a symmetrical decrease in frequency for values above and below the mean, forming a bell-shaped curve.

What are parental gametes?

In a test cross, the gametes that come from the parents of the heterozygous organism, those that are not the result of recombination or crossing over and are produced more frequently.

What is a map unit?

A unit for measuring genetic linkage.

How is the sex of any offspring determined?

The type of male gamete (X or Y) that fertilizes the female gamete (always X).

Males produce gametes with either an X or a Y chromosome with equal frequency.

Why are males more likely to exhibit the sex-linked recessive trait?

They only carry a single X chromosome.

Since females carry two X chromosomes, they need two recessive alleles in order to exhibit the recessive trait.

What is red-green colour blindness?

A general term for a spectrum of relativity common sex-linked recessive disorders including protan and deutan deficiency.

What is protan deficiency?

Caused by reduced numbers or a complete absence of red photoreceptors in the eye, which results in reduced visibility and darkening or reds.

More common in males.

What is deutan deficiency?

Caused by reduced numbers or a complete absence of green photoreceptors in the eye, which results in reduced visibility of greens.

More common in males.

How are sex-linked traits written?

The sex chromosome is written as a capital letter and the genes are written in superscript next to each X chromosome. (X X for female and X Y for male) The Y chromosome does not carry a gene.

What is Huntington’s disease?

A disease that causes degeneration of brain cells resulting in deterioration of physical and mental abilities.

What is albinism?

A disorder caused by an autosomal recessive allele, resulting in a lack of pigment in hair, skins, or eyes.

How to calculate the percentage recombination. (map units)

total number of recombinants divided by the total number of offspring times 100. the answer will be a percentage that is the map unit answer as well (30% = 30 map units)