Inheritance in action

Inheritance in actionI can explain how sex (gender) is determined in humans.I can predict what features a child might inherit.How many chromosomes do humans have?46or 23 homologous pairs23 from Mom and 23 from DadHow many chromosomes determined whether you were a boy or a girl?

The Sex chromosomes

If you get a Yyoure a boy.Its all down toDad.

The Sex chromosomes

If you get an Xyoure a girl.

Its all down toDad.Punnett SquaresProf. Reginald Crundall Punnett1875-1967 XXXYXXXXXYXYQuestionsTwins are born. Twin A is XY and twin B is XX. What sex are the two babies?How is your gender decided by chromosomes?What other characteristics could we predict for?Tongue rollingDangly earlobes

Eye colourCleft ChinHair colour

A characteristic is controlled by the two forms of a gene present in an individual. These are called alleles.DimplesCould we calculate a probability on what we would expect to see?But to understand this we need to add some new words to our glossary.Yesthe set of genes (alleles) that an organism possessesGenotypephysical appearance of an organism.Phenotypewhen two alleles (gene types) are identicalHomozygouswhen the two alleles are differentHeterozygousAlleledifferent forms of the same gene

allele which controls the characteristic whenever it is present. Dominantallele whose characteristics only show up when it is present on both chromosomesrecessiveBB or BbbbDimplesThe allele for dimples (D) is dominant over the allele for no-dimples (d).DDddDdDdDdDd

Probability of a child with dimples100%Dimplesdddddddddddd

Probability of a child with dimples0%The allele for dimples (D) is dominant over the allele for no-dimples (d).DimplesThe allele for dimples (D) is dominant over the allele for no-dimples (d).DdDdDDDdDddd

Probability of a child with dimples75%DimplesThe allele for dimples (D) is dominant over the allele for no-dimples (d).DdddDdddDddd

Probability of a child with dimples50%AlbinismThe allele for normal melanin (M) is dominant over the allele for albinism (m).MmMmMMMmMmmmProbability of a child with albinism25%

EarwaxThe allele for wet earwax (W) is dominant over the allele for dry earwax (w).WwwWwWwWwWwProbability of a child with dry earwax0%W

PolydactylyThe allele for six fingers (P) is dominant over the allele for five fingers (p).PppPpppPpppProbability of a child with six fingers50%p

Questions1. What is a dominant allele?2. What is a recessive allele?4. If a heterozygous man with dimples fathers a child with a woman with no dimples what is the probability of a child with dimples?3. What does homozygous and heterozygous mean?

Stretch your mindUsing the Internet:Look for further examples of inherited characteristics (in man and other species). Contrast how pattern of inheritance is effected when linked to sex chromosome.Investigate arguments why many classic Mendelian traits have been discredited and are now thought to be much more complicated. *Theme Tunes**Theme Tunes*Other29910.42eng - 000000E6 0000012E 0000086C 0000099F 00000ACC 00000ACC 00002673 00002A4E 00003A00 00000ACC