inheritance

KS4 Biology : 

KS4 Biology Inheritance

Contents : 

Inheritance Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross

Inheritance introduction : 

the definition of certain genetic terms, Inheritance introduction To understand how inheritance works you need to know: and 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.

Homologous chromosomes : 

© Boardworks Ltd 2004 Homologous chromosomes In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents. Chromosomes are matched in pairs that contain one chromosome inherited from each parent. So are the genes in a matching pair of chromosomes exactly the same? chromosome from female parent chromosome from male parent

Different versions of genes : 

Each chromosome may have a different version of a gene. Different versions of a gene, that code for different versions of a characteristic, are called alleles. 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 petals version for red petals gene for petal colour gene for petal colour

Pairs of alleles – homozygous : 

Pairs of alleles – homozygous If the alleles in a matching pair are the same, they are called homozygous alleles. 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.)

Pairs of alleles – heterozygous : 

Pairs of alleles – heterozygous If the alleles in a matching pair are different, they are called heterozygous alleles. Which characteristic is expressed if alleles are different? Some alleles are dominant to other forms of a gene and will 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.)

Representing alleles : 

Representing alleles Letters are used to represent different alleles. 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. = =

Genotypes and phenotypes : 

Genotypes and phenotypes The 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: RR Rr rr (Click twice on each bud to reveal the flowers; click again to close them.)

Genetic jargon : 

Genetic jargon gene allele phenotype genotype Section 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 alleles. What do these genetic terms mean?

Genetic jargon : 

homozygous heterozygous recessive dominant Pair 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 both 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 jargon What do these genetic terms mean?

Matching pairs – genes : 

© Boardworks Ltd 2004 Matching pairs – genes

Matching pairs – characteristics : 

Matching pairs – characteristics

Contents : 

Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross Inheritance

RR x rr – crossing homozygous parents : 

x phenotype: genotype: RR rr Homozygous means that both alleles of a gene are 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 parents What are the possible offspring of a cross between a homozygous red flower and a homozygous yellow flower?

RR x rr – F1 offspring : 

RR x rr R R r r parental genotype: gametes: r r R R Rr Rr Rr Rr F1 offspring genotype: RR x rr – F1 offspring What are the phenotypes of the F1 offspring? ?

RR x rr – F1 phenotypes : 

F1 genotypes: RR x rr – F1 phenotypes Rr Rr Rr Rr F1 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) RR x rr parental genotype:

Homozygous cross activity : 

© Boardworks Ltd 2004 Homozygous cross activity

Contents : 

Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross Inheritance

Rr x Rr – crossing heterozygous parents : 

The 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 generation genotype: phenotype: X Rr Rr Rr x Rr – crossing heterozygous parents

Rr x Rr – F2 offspring : 

Rr x Rr – F2 offspring R r R r RR Rr Rr rr What are the phenotypes of the F2 offspring? ? parental genotype: Rr x Rr R r R r gametes: F2 offspring genotype:

Rr x Rr – F2 phenotypes : 

Rr x Rr – F2 phenotypes F2 genotypes: RR Rr Rr rr F2 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) In the F2 generation, 3 of the 4 possible offspring are red. Only one offspring shows the recessive phenotype. When two heterozygous parents are crossed, the possible offspring will always show a 3:1 ratio in favour of the dominant phenotype. parental genotype: Rr x Rr

Heterozygous cross activity : 

© Boardworks Ltd 2004 Heterozygous cross activity

Contents : 

Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross Inheritance

What is a test cross? : 

What is a test cross? A test cross allows you to find out if an organism showing a dominant characteristic is homozygous or heterozygous for the dominant allele. For example the genotype of a red flower could be: RR or Rr What could you cross a red flower with to find its genotype?

Carrying out a test cross : 

A test cross is carried out between the flower of unknown genotype and another flower whose genotype is known. For example, a yellow flower can only have the genotype rr because it’s recessive. So the test cross is: x ? (RR or Rr) rr Carrying out a test cross

Test cross – 2 types : 

Test cross – 2 types If the red flower is homozygous (RR) then the cross is the same as the first cross (RR x rr). All of the offspring will be heterozygous and have red petals. What about the other possible cross between a heterozygous red flower (Rr) and yellow flower (rr)? rr x ? (RR or Rr)

Test cross offspring : 

Test cross offspring R r r r gametes: offspring genotype: r r R r Rr Rr rr rr What are the phenotypes of these offspring? ? Rr x rr parental genotype:

Test cross results : 

Test cross results F2 genotypes: Rr Rr rr rr F2 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) Rr x rr parental genotype:

Test cross activity : 

© Boardworks Ltd 2004 Test cross activity

Contents : 

Contents All about alleles Homozygous cross Using a test cross Co-dominance Heterozygous cross Inheritance

What is co-dominance? : 

RR WW What is co-dominance? For example, let’s assume that the red allele (R) and the white allele (W) are co-dominant: x

Co-dominance cross – offspring : 

RR x WW R R W W parental genotype: gametes: offspring genotype: R R W W RW RW RW RW The alleles are co-dominant so both are expressed. What will the offspring flowers look like? Co-dominance cross – offspring ?

Co-dominance cross – phenotypes : 

RW RW RW RW Co-dominance cross – phenotypes offspring genotypes: offspring phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) RR x WW parental genotype:

Co-dominance activity : 

© Boardworks Ltd 2004 FLASH 5 – Blood groups Co-dominance activity

Inheritance multiple-choice quiz : 

Inheritance multiple-choice quiz