Monohybrid inheritance Learning objectives Define the terms dominant

Monohybrid inheritance Learning objectives: • Define the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance • Describe patterns of monohybrid inheritance using a genetic diagram • Predict probabilities of outcomes from monohybrid crosses • Interpret family pedigrees

Alleles Task 1: Recall the definition for an allele. gene for petal colour version for red petals version for yellow petals

Alleles Task 1: Recall the definition for an allele. gene for petal colour version for red petals version for yellow petals Different versions of a gene, that code for different versions of a characteristic, are called alleles.

Homozygous If the alleles in a matching pair are the same, they are called homozygous alleles. allele for yellow petals allele for red petals Task 2: What colour are the flowers with these homozygous pairs of alleles? (Click twice on each bud to reveal the flower; click again to close them. )

Heterozygous If the alleles in a matching pair are different, they are called heterozygous alleles. allele for red petals allele for yellow petals Some alleles are dominant to other forms of a gene and will always be expressed, even if an individual only has one copy of the allele. A recessive allele will only be expressed in a homozygous form (if the individual has two copies of the recessive allele). Task 3: Which is the dominant allele in this heterozygous pair? Task 4: Which is the recessive allele in this heterozygous pair?

Representing alleles Letters are used to represent different alleles. A dominant allele is always a CAPITAL LETTER. allele for red petals = R A recessive allele is always the corresponding small letter. allele for yellow petals = r The allele pair for each characteristic is called the genotype. The physical expression of an allele pair is the phenotype.

Representing alleles Task 5: What are the phenotypes of these genotypes? genotype: phenotype: (Click twice on each bud to reveal the flowers; click again to close them. ) RR rr Rr

Monohybrid inheritance is the inheritance of a single gene. Genetic diagrams and punnett squares can be used to describe patterns and predict probabilities of outcomes of monohybrid crosses.

Monohybrid inheritance Punnett squares can be used to describe patterns and predict probabilities of outcomes of monohybrid crosses. Monohybrid cross between heterozygous plants

Monohybrid inheritance Punnett squares can be used to describe patterns and predict probabilities of outcomes of monohybrid crosses. Monohybrid cross between heterozygous plants Mother’s alleles → R r

Monohybrid inheritance Punnett squares can be used to describe patterns and predict probabilities of outcomes of monohybrid crosses. Monohybrid cross between heterozygous plants Mother’s alleles → Father’s alleles ↓ R r

Monohybrid inheritance Punnett squares can be used to describe patterns and predict probabilities of outcomes of monohybrid crosses. Monohybrid cross between heterozygous plants Mother’s alleles → Father’s alleles ↓ R r R RR Rr rr

Monohybrid inheritance Brown eyes (B) are dominant over blue eyes (b) Task 6: Draw a punnett square for a cross between a homozygous brown eyed Father and a blue eyed Mother’s alleles → Father’s alleles ↓

Monohybrid inheritance Brown eyes (B) are dominant over blue eyes (b) Task 6: Draw a punnett square for a cross between a homozygous brown eyed Father and a blue eyed Mother’s alleles → Father’s alleles ↓ b b B Bb Bb

Co-dominance Sometimes two alleles are equally dominant to each other. In genetics, this is called co-dominance and means that neither allele is recessive to the other allele. Co-dominant alleles are both expressed in the phenotype.

Co-dominance

Family pedigrees Doctors can use a pedigree analysis chart to show genetic disorders are inherited in a family. They can use this to work out the probability (chance) that someone in a family will inherit a condition. This is called pedigree analysis.

What's the chance of the offspring having cystic fibrosis?

What's the chance of the offspring having polydactyly?

Family pedigrees

Task 7: What is this condition?

Albinism is a genetic disorder caused by a recessive allele (a) which is characterised by lack of pigment in skin, hair and eyes (white skin/fur and red eyes) Task 8: What is the genotype of a sufferer? aa Albinism occurs in many species, but it is more common in humans. Task 9: Explain why albinism is more common in humans. Albinism is not as detrimental to the survival of humans as it is for other species. For example, some species would not be camouflaged and therefore more likely to be killed by a predator, and hence not pass on the allele for albinism.

Albinism a A albino trait normal allele Task 10: 1. What are the genotypes of parents A (3 & 4)? Explain how you know. . . 1. What are the genotypes of 15, 16 and 17? Explain how you know. .

Thumbs up or down Learning objectives: • Define the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance • Describe patterns of monohybrid inheritance using a genetic diagram • Predict probabilities of outcomes from monohybrid crosses • Interpret family pedigrees