KS4 Inheritance课件

1、 Boardworks Ltd 20041 of 36KS4 BiologyInheritance Boardworks Ltd 20042 of 36Inheritance Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross Boardworks Ltd 20043 of 36l the definition of certain genetic terms, Inheritance introductionTo understand how inheri

2、tance works you need to know:land how to use genetic crosses to determine the characteristics of offspring.In this unit, petal colour is used to show how characteristics are inherited in offspring. Boardworks Ltd 20044 of 36Definition to remember: Chromosomes- is a thread of DNA made up of genes. Ge

3、ne- a length of DNA that codes for a protein. Allele-is a version of a gene. Letters are used to represent this: AA or Aa etc. Homozygous alleles that are identical; example AA or aa or BB or bb. Heterozygous alleles that are different; example Aa or Bb. Boardworks Ltd 20045 of 36Definitions continu

4、es: Dominant allele (AorB) is always expressed in the phenotype. Recessive allele(a or b) is only expressed when no dominant allele is present. Phenotype- is ALL features of the organism that is visible (eye colour). Genotype- is the genetic makeup of the organism. The alleles the organism has, like

5、 AA, bb, cc, DD or Rr Boardworks Ltd 20046 of 36 Boardworks Ltd 2004 Homologous chromosomesIn all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents. Chromosomes are matched in pairs that containone chromosome inherited from each parent.So are t

6、he genes in a matching pair of chromosomes exactly the same?chromosome from female parentchromosome from male parent Boardworks Ltd 20047 of 36Each chromosome may have a different version of a gene. Different versions of a gene, that code for different versions of a characteristic, are called allele

7、s.The chromosomes in a matching pair contain the same type of genes that code for the same characteristics. Different versions of genes version for yellow petalsversion for red petalsgene for petal colourgene for petal colour Boardworks Ltd 20048 of 36 Pairs of alleles homozygousIf the alleles in a

8、matching pair are the same, they are called homozygous alleles.allele for yellow petalsallele for yellow petalsallele for red petalsallele for red petalsWhat colour are the flowers with these homozygous pairs of alleles?(Click twice on each bud to reveal the flower; click again to close them.) Board

9、works Ltd 20049 of 36 Pairs of alleles heterozygousIf the alleles in a matching pair are different, they are called heterozygous alleles.Which characteristic is expressed if alleles are different?allele for yellow petalsallele for red petalsSome alleles are dominant to other forms of a gene and will

10、 always be expressed.Which is the dominant allele in this heterozygous pair? Which is the recessive allele in this heterozygous pair? (Click twice on the bud to reveal the flower; click again to close it.) Boardworks Ltd 200410 of 36 Representing allelesLetters are used to represent different allele

11、s.The allele pair for each characteristic is called the genotype.What colour are flowers with the genotype Rr? A dominant allele is always a capital letter.A recessive allele is always the corresponding small letter.allele for red petalsRallele for yellow petalsr= Boardworks Ltd 200411 of 36 Genotyp

12、es and phenotypesThe allele pair for each characteristic is called the genotype.The physical expression of an allele pair is the phenotype.What are the phenotypes of these genotypes?genotype:phenotype:RRRrrr(Click twice on each bud to reveal the flowers; click again to close them.) Boardworks Ltd 20

13、0412 of 36 Genetic jargongeneallelephenotypegenotypeSection of DNA that codes for a particular trait or characteristic.A different form of a gene that codes for a different version of a characteristic.A description of the pair of alleles present for a characteristic.The physical expression of the al

14、leles.What do these genetic terms mean? Boardworks Ltd 200413 of 36homozygousheterozygousrecessivedominantPair of alleles that produce a characteristic that are the same, e.g. HH. Pair of alleles that produce a characteristic that are different, e.g. Hh.An allele that will only be expressed when bot

15、h alleles are of this type, represented by a lower case letter.An allele that will always be expressed even when there is only one of these alleles present, represented by a capital letter. Genetic jargonWhat do these genetic terms mean? Boardworks Ltd 200414 of 36 Boardworks Ltd 2004 Matching pairs

16、 genes Boardworks Ltd 200415 of 36 Matching pairs characteristics Boardworks Ltd 200416 of 36 Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous crossInheritance Boardworks Ltd 200417 of 36xphenotype:genotype:RRrrHomozygous means that both alleles of a gene are

17、the same.Red is the dominant allele for these flowers, so the alleles for petal colour are: red = R , yellow = r. RR x rr crossing homozygous parentsWhat are the possible offspring of a cross between a homozygous red flower and a homozygous yellow flower? Boardworks Ltd 200418 of 36RRx rrRRrrparenta

18、l genotype:gametes:rrRRRrRrRrRrF1 offspringgenotype: RR x rr F1 offspringWhat are the phenotypes of the F1 offspring? Boardworks Ltd 200419 of 36F1 genotypes: RR x rr F1 phenotypesRrRrRrRrF1 phenotypes:(Click twice on the buds to reveal the flowers; click again to close them.)The possible offspring

19、of a cross between two homozygous parents are always heterozygous and so the dominant characteristic is always expressed in this generation.RRx rrparental genotype: Boardworks Ltd 200420 of 36 Boardworks Ltd 2004 Homozygous cross activity Boardworks Ltd 200421 of 36 Contents All about alleles Homozy

20、gous cross Using a test cross Co-dominance Heterozygous crossInheritance Boardworks Ltd 200422 of 36The offspring (Rr) from the first cross (RR x rr) are called the F1 generation. What happens in a cross between these offspring?Both parent plants are now heterozygous, so the alleles in each plant are different.F1 generationgenotype:phenotype:XRrRr Rr x Rr crossing heterozy