CAS BI 107 Lecture Notes - Lecture 3: Letter Case, Allele, Gamete

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30 Oct 2018

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Define genotype, phenotype, dominant allele, recessive allele, codominant alleles,

locus, homozygous, heterozygous, carrier and test cross

Genotype: The allele combination of an organism

Phenotype:  The characteristics of an organism (determined by a combination of

genotype and environmental factors)

Dominant Allele: An allele that has the same effect on the phenotype whether it is

present in the homozygous or heterozygous state

Recessive Allele:  An allele that only has an effect on the phenotype when present

in the homozygous state

Codominant Alleles: Pairs of alleles that both affect the phenotype when present in

a heterozygote

Locus:  The particular position on homologous chromosomes of a gene

Homozygous: Having two identical alleles of a gene

Heterozygous: Having two different alleles of a gene

Carrier:  An individual that has one copy of a recessive allele that causes a genetic

disease in individuals that are homozygous for this allele

Test Cross: Testing a suspected heterozygote by crossing it with a known

homozygous recessive

Determine the genotypes and phenotypes of the offspring of a monohybrid cross

using a Punnett grid

A genetic cross is a means of determining the genetic characteristics of potential

offspring based on the genetic characteristics of the prospective parents

A monohybrid cross determines the allele combinations of offspring for one particular

gene only (HL students may refer to topic 10.2 for dihybrid crosses)

Monohybrid crosses can be

calculated according to the following

steps:

Step 1:  Designate characters to

represent the alleles

■Capital letter for dominant

allele, lower case letter for recessive

allele

Step 2: Write down the genotype

and phenotype of the parents

■This is the P generation

(parental generation)

Step 3:  Write down the genotype of

the parental gametes

■These will be haploid as a

result of meiotic division

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Step 4: Use a Punnett grid to work out the potential gamete combinations

■As fertilisation is random, all combinations have an equal probability

Step 5:  Write out the genotype and phenotype ratios of potential offspring

■This is the F1 generation (first filial generation)

■Subsequent generations through interbreeding labeled F2, F3, etc.

Note:  The genotypic and phenotypic ratios calculated are only probabilities

4.3.3 State that some genes have more than two alleles (multiple alleles)

Some genes have more than two alleles for a given trait (e.g. the ABO blood group

system)

The alleles which are not recessive may either:

■Share codominance (be expressed equally in the phenotype)

■Share incomplete dominance (neither is fully expressed in the phenotype,

resulting in blending)

■Demonstrate a dominance order (e.g. allele A > allele B > allele C)

4.3.4 Describe ABO blood groups as an example of codominance and multiple

alleles

When assigning alleles for codominance, the convention is to use a common letter to

represent dominant and recessive and use superscripts to represent the different

codominant alleles

■I stands for immunoglobulin (antigenic protein on blood cells)

■A and B stand for the codominant variants

The ABO gene has three alleles: IA, IB and i

■IA and IB are codominant, where as i is recessive (no antigenic protein is

produced)

■Codominance means that both IA and IB alleles will be expressed within a

given phenotype

The genotypes and phenotypes of the ABO blood groups are:

The ABO Blood Group System

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Document Summary

The particular position on homologous chromosomes of a gene. The characteristics of an organism (determined by a combination of. An allele that has the same effect on the phenotype whether it is. An allele that only has an effect on the phenotype when present. Pairs of alleles that both affect the phenotype when present in. Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross. Dominant allele: present in the homozygous or heterozygous state. Carrier: disease in individuals that are homozygous for this allele. Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a punnett grid. A genetic cross is a means of determining the genetic characteristics of potential offspring based on the genetic characteristics of the prospective parents. A monohybrid cross determines the allele combinations of offspring for one particular gene only (hl students may refer to topic 10. 2 for dihybrid crosses)

Related Questions

When a parent who is heterozgyous for a trait is crossed with a parent who is heterozygous for a trait, the offspring will:

(remember homozygous means two of the same alleles and heterozygous means two different alleles)

Select one:

a. have 3 out of 4 the dominant phenotype and 1 out of 4 the recessive phenotype

b. have 2 out of 4 the dominant phenotype and 2 out of 4 the recessive phenotype

c. all have the dominant phenotype

d. have 1 out of 4 the dominant phenotype

When a parent who is heterozgyous for a trait is crossed with a parent who is homozygous dominant for a trait, the offspring will:

(remember homozygous means two of the same alleles and heterozygous means two different alleles)

Select one:

a. all have the recessive phenotype

b. all will have the dominant allele

c. all be homozygous dominant genotype

When a parent who is heterozgyous for a trait is crossed with a parent who is heterozygous for a trait, the offspring will:

(remember homozygous means two of the same alleles and heterozygous means two different alleles)

Select one:

a. have 3 dominant phenotypes, 2 heterozygous genotypes, and 1 homozygous recessive genotype

b. have 1 dominant phenotype, 2 heterozygous genotypes, and 1 homozygous recessive phenotype

c. have all dominant phenotypes, 2 heterozygous genotypes, and 1 homozygous recessive genotype

When doing Punnett squares for fur, the letter f represents ______ and the letter F represents _____.

Select one:

a. the recessive allele, the dominant allele

b. the dominant allele, the recessive allele

c. the dominant gene, the recessive gene

d. the recessive gene, the dominant gene

10.

When a parent who is heterozgyous for a trait is crossed with a parent who is homozygous recessive for a trait, the offspring will:

(remember homozygous means two of the same alleles and heterozygous means two different alleles)

Select one:

a. be half heterozygous and half homozygous recessive

b. be all heterozygous

c. be all homozygous recessive

d. be all homozygous dominant

Differentiate between asexual and sexual reproduction, and explain the advantages and disadvantages of each.

Differentiate between dominant and recessive alleles, and describe how they are expressed in homozygous, heterozygous, and recessive states.

Distinguish between phenotype and genotype. Which of them interacts directly with the environment? When would a mutation in only one allele affect the phenotype of a diploid organism? When would a mutation in only one allele affect adaptation to a changing environment?

Distinguish between a gamete and a zygote.