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Genetics & Inheritance

Genetics & Inheritance. Chromosomes come in pairs. Homologous Chromosomes. The Human Karyotype Contains 23 Pairs of Chromosomes. The Human Karyotype Contains at Least 22 Pairs of HOMOLOGOUS Chromosomes. Humans have 1 Pair of SEX CHROMOSOMES. =23 Pairs of Chromosomes.

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Genetics & Inheritance

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  1. Genetics & Inheritance

  2. Chromosomes come in pairs Homologous Chromosomes

  3. The Human Karyotype Contains 23 Pairs of Chromosomes The Human Karyotype Contains at Least 22 Pairs of HOMOLOGOUS Chromosomes

  4. Humans have 1 Pair of SEX CHROMOSOMES =23 Pairs of Chromosomes The Human Karyotype Contains at Least 22 Pairs of HOMOLOGOUS Chromosomes Humans have 22 Pairs of AUTOSOMES

  5. Homologous Chromosomes are not always identical in DNA sequence but contain the same genes They encode for the same traits Chromosomes Carry Genes The Human Karyotype Contains at Least 22 Pairs of HOMOLOGOUS Chromosomes A gene is a DNA sequence (part of the chromosome) that codes for a trait Different copies of genes that may vary in sequence are termed ALLELES

  6. MOM Humans are DIPLOID—Their Karyotype Contains 2 Copies of Each Gene DAD The Exception to This May be on the Sex Chromosomes. While Females Have 2 Copies of the X Chromosome (and therefore 2 copies of each gene on the X chromosome), Males Have Only 1 X Chromosome that is ‘Paired’ with 1 Y Chromosome Different forms of genes that may vary in sequence are termed ALLELES

  7. MOM Humans are DIPLOID—Their Karyotype Contains 2 Copies of Each Gene DAD Different forms of genes that vary in sequence are termed ALLELES If the 2 copies/alleles code for identical gene products, the individual is said to be HOMOZYGOUS If the 2 copies/alleles code for non-identical gene products, the individual is said to be HETEROZYGOUS

  8. Mom Dad Dad Mom

  9. MOM Humans are DIPLOID—Their Karyotype Contains 2 Copies of Each Gene DAD Meiosis Separates Alleles

  10. DIPLOID 2 Short chromosomes 2 long chromosomes Meiosis (Happens in Ovaries and Testes)

  11. DIPLOID Meiosis (Happens in Ovaries and Testes) HAPLOID Egg & Sperm (Sex Cells, Gametes)

  12. MOM Humans are DIPLOID—Their Karyotype Contains 2 Copies of Each Gene DAD Different forms of genes that vary in sequence are termed ALLELES If the 2 copies/alleles code for identical gene products, the individual is said to be HOMOZYGOUS If the 2 copies/alleles code for non-identical gene products, the individual is said to be HETEROZYGOUS

  13. Dominance Refers to Phenotype Outwardly Observable Traits are Known as an Individual’s PHENOTYPE Phenotype Depends Upon an Individual’s GENOTYPE Genotype is the set of genes that an individual possesses.

  14. Alleles Can Be Dominant or Recessive Humans are DIPLOID—Their Karyotype Contains 2 Copies of Each Gene If the 2 copies are not identical—an individual is heterozygous—one copy may be more ‘assertive’ in its expression than the other; the product of one version of the gene (one allele) may ‘mask’ the visibility of the other. If Wild Type is DOMINANT… If Mutant is DOMINANT… Wild Type Wild Type Mutant Mutant Mutant …Mutant is RECESSIVE WILD TYPE MUTANT

  15. GAMETES Inheritance is Predictable If Parental Genotypes are Known, Inheritance is Predictable Inheritance Depends Upon What Version of Allele is Provided by Each Parent, and How Those Alleles Interact with One Another

  16. Tay-Sachs Disease Tay-Sachs Disease is a neurodegenerative disease. Inheriting two non-functional copies of a gene for a protein that normally breaks down certain membrane lipids causes those lipids to build up in cells. As a result, neurons die. Neuronal death causes a progressive deterioration of mental and physical abilities that commences around six months of age and usually results in death by the age of four. There is no known cure or treatment.

  17. MOM DAD Tay-Sachs Disease If Mom Carries a Mutant Allele and Dad is Normal… Mom Provides Either a Normal or Mutant Allele in her egg Dad Provides a Normal Allele in his sperm MOM 50% of Their Offspring Will be ‘Carriers’ of Tay-Sachs Disease—They will be phenotypically normal and genotypically heterozygous DAD 50% of their offspring will be both phenotypically and genotypicallynormal

  18. Tay-Sachs Disease If Both Mom and Dad Carry a Mutant Allele… Mom Provides Either a Mutant Allele or a Normal Allele Dad Provides Either a Mutant Allele or a Normal Allele MOM 25% of Their Offspring will be Phenotypically and Genotypically Normal 50% of Their Offspring will be Carriers Of the Disease (Heterozygous)—Phenotypically Normal DAD 25% of Their Offspring will have Tay-Sachs Disease

  19. Phenotypic ratio = 3:1 3 with freckles, 1 without Genotypic ratio = 1:2:1 1 homozygous for freckles 2 heterozygous for freckles 1 homozygous for no freckles

  20. Genetics Vocabulary Homologous Chromosomes Allele Autosomes Sex Chromosomes Diploid Homozygous Heterozygous Meiosis Gamete Dominant Recessive Genotype Phenotype

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