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Year 10 ScienceGenetics

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Genetics outcomesThis unit will cover:• History• Chromosomes and genes• Genetics problem solving• Human inheritance• DNA

To gain a satisfactory for this unit:1. Keep a careful record of all theory and related activities2. Participate in practical work and complete a written record3. Complete a research task4. Complete a test or exam

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What is genetics?

• Genetics is the study of heredity

• Animals, plants and micro-organisms are studied

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History

• Gregor Mendel – father of genetics • Monk in Austria in 1856• Studied peas in the monastery garden

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Mendel’s results

Parent round pea X wrinkled pea

F1 all round peas

F1 crossed F1 X F1

F2 3 round : 1 wrinkled

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Mendel’s conclusions

• Round is dominant to wrinkled in peas

• Yellow is dominant to green peas

• A dominant trait masks the effect of a recessive trait

• Mendel’s scientific work was ignored for about 40 years

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Chromosomes

• Are long thread like structures found in the nucleus

• Made of a chemical called DNA

• Deoxyribonucleic acid• DNA is coiled tightly

inside a cell

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Genes

• Genes are found on chromosomes

• Genes code for particular traits

• Many thousands of genes are found on each chromosome

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Homologous chromosomes

• 2 copies of each chromosome in each body cell

• 2 copies of each gene in each cell

• Humans have 46 chromosomes in each body cell

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Chromosomes, genes and alleles

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Haploid and diploid cells

• Diploid cells have 2 copies of each chromosome eg body cells

• Haploid cells have 1 copy of each chromosome eg gametes (egg and sperm)

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Human chromosomes

• Humans have 46 chromosomes in every body cell

• 23 chromosomes in every sperm and egg

egg X sperm 23 23

zygote 46

New individual 46

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Mitosis

• The process of cell division to make new body cells

• replaces old and damaged cells

• 2n 2n• 46 46

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Meiosis

• Formation of eggs in ovary and sperm in ovary and testes

• Forms haploid cells• 2n n• Human chromosomes

46 23 in egg or sperm

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Genotype and phenotype

Let B = brown eyes, b = blue eyesB is dominant to b

• Every individual has 2 copies of each gene• The genotype of an individual is its genetic

makeup eg BB or Bb or bb• The phenotype of an individual is its outward

appearance eg blue eyes or brown eyes

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Homozygous and heterozygous

• An allele is the alternative forms of a gene eg B or b

• Homozygous individuals have the same allele on both chromosomes eg BB or bb

• Heterozygous individuals have different alleles on both chromosomes eg Bb

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Homozygous X homozygous

Let B = brown eyes, b = blue eyesB is dominant to b

P phenotype brown eyes X blue eyesP genotype BB X bbGametes B b

F1 genotype Bb

F1 phenotype All brown eyes

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Heterozygous X homozygous

P phenotype brown eyes X blue eyes

P genotype Bb X bb

Gametes B, b b

F1 genotype ½Bb, ½bb

F1 phenotype ½brown eyes, ½blue eyes

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Heterozygous X heterozygous

P phenotype brown eyes X brown eyesP genotype Bb X BbGametes B, b B, b

F1 genotype ¼BB , ½Bb, ¼ bb

F1 phenotype ¾brown eyes, ¼ blue eyes

gametesB b

B BB Bb

b Bb bb

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Co-dominance

• In co-dominance, the phenotype of the heterozygote is a combination of the homozygous individuals

• Roan cattle

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Incomplete dominance

• The heterozygote is intermediate between the two homozygous organisms

• Snap dragons colours