BIOL1003 Lecture Notes - Lecture 15: Phenotype, Allele, Mendelian Inheritance
Define the relationship of genotype and phenotype
Genotype determines phenotype
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e.g. Tt, TT, tt
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Genotype - genetic makeup of an organism, specific allelic composition
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Phenotype - set of detectable characteristics or traits of an organism, appearance
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e.g. AA or Aa = normal pigmentation, aa = albinism phenotype
15a)
Sunday, 4 June 2017
4:04 PM
15. Inheritance Page 1
Define alleles, heterozygosity and homozygosity
Each chromosome contains genes
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Each gene codes for characteristic, determines proteins in a cell
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Genes - discrete hereditary factors that determine traits
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Locus - position of gene on a chromosome
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Allele
Different forms of a gene on homologous chromosomes
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e.g. Aa, aa, AA
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Dominant allele - produces normal enzymes, appears in phenotype
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Recessive - produces abnormal enzyme, does not appear in phenotype
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Heterozygous
2 alleles are slightly different for one trait
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e.g. Aa
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Homozygous
2 alleles are identical for one trait
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e.g. aa
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Genome
All genes in one homologous set of 23 chromosomes in one individual
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15b)
Sunday, 4 June 2017
11:07 PM
15. Inheritance Page 2
Describe meiosis and the consequences of recombination
During meiosis, chromosomes distributed so each gamete receives only one chromosome
from each homologous pair
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Recombination
Pair of sex chromosomes separates so each secondary oocyte receives one X chromosomes,
whereas each sperm cell receives either an X or Y chromosome
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Genes on a given chromosome linked, so tend to be inherited as a set rather than as
individual genes because chromosomes segregate during meiosis
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Homologous chromosomes may exchange genetic info by CROSSING OVER in prophase
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Resulting zygote has 47 or 46 chromosomes instead of 46
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Segregation errors may occur, as homologous pair may not segregate e.g. one daughter
cell receives both chromosomes, while the other receives none
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Random distribution of genes
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15c)*
Monday, 5 June 2017
1:15 PM
15. Inheritance Page 3
Document Summary
Genotype - genetic makeup of an organism, specific allelic composition e. g. tt, tt, tt. Phenotype - set of detectable characteristics or traits of an organism, appearance e. g. aa or aa = normal pigmentation, aa = albinism phenotype: inheritance page 1. Each gene codes for characteristic, determines proteins in a cell. Genes - discrete hereditary factors that determine traits. Locus - position of gene on a chromosome. All genes in one homologous set of 23 chromosomes in one individual: inheritance page 2. During meiosis, chromosomes distributed so each gamete receives only one chromosome from each homologous pair. Pair of sex chromosomes separates so each secondary oocyte receives one x chromosomes, whereas each sperm cell receives either an x or y chromosome. Genes on a given chromosome linked, so tend to be inherited as a set rather than as individual genes because chromosomes segregate during meiosis. Homologous chromosomes may exchange genetic info by crossing over in prophase.