D3.2 Inheritance

D3.2.1

• Gamete: Reproductive cells of an organism

• Zygote: Fertilized egg cell - egg + sperm

• Diploid: 2 sets of all chromosomes, contains homologous pairs

  • 2 copies of each autosomal gene

• Haploid: 1 set of chromosomes

D3.2.2 Genetic crosses in plants

• P: Parent generation

• First offspring: F1

• Offspring of F1: F2

• Pollen is transferred from anthers of male parent to stigmas of female parent

  • using a brush

D3.2.3 Genotype as the combination of alleles in an organism

• Genes: A sequence of DNA nucleotides that codes for a protein product

• Alleles: Variations of the same gene

• Homozygous: Genotype with the same allele

• Heterozygous: Genotype with different alleles

D3.2.4 Phenotype as observable traits

• Genotype: Genetic makeup of an organism (genes, alleles, etc.)

• Phenotype: Observable, physical traits

  • Susceptible to change

D3.2.4 Dominant and recessive alleles

• Dominant allele: If present in the genotype will be the one expressed

  • Codes for functional protein

• Recessive allele: Will only be expressed if present as homozygous recessive

  • Codes for malfunctioning protein

• Recessive alleles are often mutations of dominant alleles

D3.2.5 Phenotypic Plasticity

• The ability of an organism’s phenotype to change according to the environmental conditions

• e.g. Hydrangea color - soil pH

• e.g. Arctic fox fur - sun exposure

• e.g. height

D3.2.7 Phenylketonuria

• Genetic illness - recessive allele in chromosome 24

• Carrier: Heterozygous - carries allele for disease but doesn’t express symptoms

• Rare - parents must both be carriers - only 25%

• Phenylketonuria

  • Malfunctioning PAH gene - changes phenylalanine to tyrosine

  • Body cannot break down phenylalanine

  • Impairs brain development

D3.2.8 Single-nucleotide polymorphisms and multiple alleles in gene pools

• New alleles of a gene are a result of mutation

• Single nucleotide polymorphisms

  • variation at a single position in the DNA sequence

  • more common in the population

• Gene pool: All the genes of all individuals in a sexually reproducing population

• Many different alleles can exist in a gene pool, but each individual only has 2 different alleles

D3.2.9 ABO Blood groups

• Type AB - Codominance

  • Both A and B alleles are dominant

  • Expressed simultaneously

• O: Recessive allele

• Glycoprotein in the membrane of red blood cells → blood type

  • A → addition of acetylgalactosamine

  • B → addition of galactose

  • O → Normal glycoprotein

D3.2.10 Incomplete dominance and codominance

• Incomplete dominance

  • Traits with 2 alleles

    • neither dominant or recessive

  • e.g. 4 o’clock flower

    • red allele + white allel → pink flower

    • alleles mix to form hybrids

D3.2.11 Sex determination in humans and inheritance of genes on sex chromosomes

• X chromosome

  • Relatively large

  • Centromere near the middle

  • Essential for life - all humans must have at least one

• Y chromosome

  • Much smaller

  • Centromere near one end

  • Only for males

• Female: XX

• Male: XY

• SRY

  • Gene on the Y chromosome

  • Causes embryonic gonads to develop into testes (TDF)

• Pleiotropy: A gene that controls a subset of genes/proteins

D2.3.12 Hemophilia as an example of a sex-linked genetic disorder

• Sex-linkage: A mutation on the sex chromosome that leads to disease

• Located on the X chromosome - recessive mutation

  • More common in males - a single mutated X chromosome causes them to show symptoms as opposed to women with 2 X chromosomes

• Blood cannot clot - don’t produce the necessary protein

D2.3.14 Continuous variation due to polygenic inheritance and/or environmental factors

• A normal distribution of variation is often due to polygenic inheritance

• Polygenic Inheritance: Phenotypes determined by numerous genes

  • e.g. height, skin color

D2.3.16 Segregation and Independent Assortment

• Segregation: Separation of alleles of a gene

• Independent assortment:

  • Segregation of the alleles of two genes so that the outcome with each gene does not affect the outcome with the other

  • genes independently separate from one another when reproductive cells develop

D2.3.18 Gene locus

• Where the gene is located on a chromosome

D2.3.19 Autosomal gene linkage

• Genes can be linked on the X chromosome - close to each other

  • Physically linked as part of the DNA of a chromosome

  • Don’t assort independently

D2.3.20 Recombinants in crosses

• Recombinant: Individual with different combination of alleles/traits from either parent

• Random orientation results in new recombinants by independent assortment

• Crossing over produces new combinations of linked genes