IB Bio Review- D3.2 Inheritance

Female (XX) only produce eggs containing the _ chromosome

X

Male (XX) can produce sperm containing either the _ or the _ chromosome

X Y

sex chromosomes are ___, and there are many genes on the x-chromosome not on the y-chromosome

non-homologous

sex-linked traits are those which are carried on the __-______ in the non-homologous region

x-chromosome

sex-linked traits are more common in ____

males

what is colorblindness?

inability or decreased ability to see color, or perceive color differences

• caused by a genetic mutation affecting the photopigments in the cones of the retina

• X-linked recessive disorder

  • since males have one X and one Y chromosome, they are more likely to be colorblind if they inherit the mutation.

  • females, with two X chromosomes, are less likely to be affected because they would need the mutation on both X chromosomes to be colorblind.

females can be _____ or _____ with respect to sex-linked genes

homozygous or heterozygous

_____ females are carriers of colorblindness and haemophilia

heterozygous

what is the genotype of a carrier female

X^N X^n

N = normal vision

n = red-green color blindness

what is the genotype of a normal male

X^N Y

(notice that there is no allele attached to the Y)

N = normal vision

n = red-green color blindness

what is blood clotting?

metabolic pathway of enzyme-controlled biochemical reactions

• requires globular proteins called clotting factors

• recessive X-linked mutations causes these factors to not be produced

what is haemophilia?

impairs the body's ability to make blood clots, a process needed to stop bleeding

• X-linked recessive disorder (carried by the X-chromosome)

  • since males have only one X chromosome, a single defective gene can cause the disorder

  • females have two X chromosomes, so a defective gene on one X chromosome is often compensated by the other X chromosome.

sex-linked, recessive:

• trait is able to skip generations

• males are predominately affected

autosomal, recessive:

• trait is able to skip generations

• no major sex-bias in expression

autosomal dominant:

• trait cannot skip generations

• no major sex-bias in expression

what is a genotype?

the combination of alleles of a gene carried by an organism

what is a phenotype?

the expression of alleles of a gene carried by an organism

what is a centromere?

joins chromatids in cell division

what is an allele?

different versions of a gene

• dominant allele = capital letter

• recessive allele = lower case letter

what is a carrier?

heterozygous carrier of a recessive disease-causing allele

what does homozygous dominant mean?

having 2 copies of the same dominant allele (AA)

what does homozygous recessive mean?

having 2 copies of the same recessive allele (aa)

• recessive alleles are only expressed when homozygous

what does codominant mean?

pairs of alleles which are both expressed when present

what does heterozygous mean?

having 2 different alleles, the dominant allele is expressed

what is gene loci?

specific position on a chromosome

who discovered the principles of inheritance with pea plant experiments?

gregor mendel, 1866

why were pea plants used for conducting genetic crosses?

• Short life cycle for generational studies.

• Can produce hybrids

• Self-pollinate

  • Easy control of pollination for experiments.

• Distinct traits for clear inheritance.

• High offspring numbers for increased data accuracy.

what are mendel’s 3 laws?

1. law of segregation

2. law of independent assortment

3. principle of dominance

what is the law of segregation?

• gametes are haploid and have 1 allele of each gene

• when male and female gamete fuse the diploid cell will have 2 alleles of each gene

• many genes have 2 allels w one dominant, one recessive, producing:

  1. AA (homozygous dominant)

  2. Aa (heterozygous)

  3. aa (homozygous recessive)

what is reductive division?

each haploid gets only one of 2 alleles parent has for each gene

what is the law of independent assortment?

• the two alleles of each gene are randomly separated into different haploid daughter nuclei during meiosis.

  • thus, the inheritance of one trait (determined by a gene) doesn't influence the inheritance of another trait (determined by a different gene).

what is the principle of dominance?

• dominant alleles always show their encoded trait when present in an organism

  • masking recessive alleles

• recessive alleles only express their encoded traits when no other alleles are present

• CODOMINANT alleles can have joint effects if both are present

_____ is the combination of alleles in an organism

genotype

____ is the observale traits of an organism

phenotype

what is phenotype plasticity?

when organisms change their gene expression pattern of proteins to become adapted to specific environmental conditions