DNA, Genes and Chromosomses Inheritance (B) DNA, Genes and Chromosomses

Learning Intention Identify factors that are due to genes and those due to environmental influences.

Genetics The study of inherited characteristics and of those factors that determine or affect inheritance.

Meet our Mr Men And our Little Misses Now lets meet their children!

Who do you think are his parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

Who do you think are his parents? Write the answers in your book.

Who do you think are his parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

What did we learn from this? Children inherit features from their parents If two parents have a certain characteristic then their child may show it even more (e.g. Mr Small + Little Miss Tiny = Mr Very Small!) Some things such as glasses, scars and muscles we get from our environment, they are not inherited.

Nucleus The nucleus carries genetic information which controls the characteristics of the organism. The structures which carry this information are called chromosomes.

Chromosomes The gene is the unit of inheritance, and each chromosome may have several thousand genes. We inherit particular chromosomes through the egg of our mother and sperm of our father. The genes on those chromosomes carry the code that determines our physical characteristics.

Physical Characteristics Some physical characteristics, like eye colour, are controlled by genes. Other physical characteristics are controlled by the environment. Can you think of a physical characteristic that isn’t controlled by genes?

Learning Intention Define the term genotype and phenotype.

Phenotypes Each of these is called a PHENOTYPE Each characteristic may display several possible traits or versions. e.g. hair colour can be brown, black or red Each of these is called a PHENOTYPE

Phenotype Leaf shape in plants, coat colour in guinea pigs, wing type in fruit flies and eye colour in humans are all examples of physical characteristics. These physical characteristics make up the organisms phenotype.

Genotype The phenotype (physical appearance) that you have is controlled by the genes that you inherit from your parents. The combination of genes that you have is called your genotype.

Genes We have two copies of every chromosome, this means we have two copies of every gene. 1st gene for eye colour 2nd gene for eye colour Chromosome 1 Chromosome 1

Alleles The different forms of a gene are called alleles. For example the gene that controls eye colour has different alleles blue, green or brown. Blue form eye gene Green form eye gene Brown form eye gene

Alleles If you inherit a blue allele from your mum and a brown allele from your dad then you will have brown eyes. This is because some alleles are DOMINANT over others.

Dominant or recessive Alleles can be dominant or recessive. Alleles which show up in the appearance of an organism are said to be dominant. Alleles which do not show up in the appearance of an organism are said to be recessive.

Dominant or recessive? Allele for white fur Allele for brown fur Which allele is dominant white fur or brown fur?

Dominant or recessive? Allele for green body Allele for yellow body Which allele is dominant green body or yellow body?

Learning Intention Be able to solve simple genetic problems.

Some definitions Genes: Phenotype: Genotype: Sections of DNA in a chromosome that control an inherited characteristic, such as, hair colour, flower colour, height, etc. The observable characteristics (appearance) of an organism. The complete set of genes possessed by an organism.

Alleles When describing an allele, we give it a letter. If it is dominant it gets a capital letter and if it is recessive it gets lower case of the same letter. e.g. in pea plants tall is dominant over dwarf, and so the tall allele is given the letter T and the dwarf allele is given t.

Alleles BB bb This mouse has two dominant brown alleles This mouse has two recessive white alleles

Alleles The genotype of the organism is the alleles it carries for that particular characteristic. The genotype for this fly is Rr, this tells us that it has one red eye allele and one white eye allele.

Alleles TT is a genotype and the plant will be tall. Tt is a genotype and the plant will be tall as T is dominant over t. tt is a genotype and the plant will be dwarf. What the plant actually looks like is called the phenotype.

Monohybrid cross A monohybrid cross is the study of the inheritance of one characteristic. Monohybrid crosses were first carried out by a monk called Gregor Mendel who worked on pea plants.

Mendel’s Pea Plant Crosses Tall plant Dwarf plant X Parent Offspring ALL Tall X F1 F2 Phenotypic Ratio 3 Tall:1 Dwarf Tall Tall Tall Dwarf

true breeding tall strain true breeding dwarf strain X parents (P) This type of experimental cross is called a monohybrid cross as it follows the inheritance of only one characteristic at a time. first filial generation (F1) all tall members of F1 self-pollinated X second filial generation (F2) F2 phenotypic ratio 3 tall : 1 dwarf

Gregor Mendel X RR rr

P X RR rr F1 Rr Rr Rr

F1 F1 X X Rr Rr F2 Red 3 White 1

Punnet square Punnet squares allow us to figure out the genotypes and phenotypes of the offspring in the F2. F1 X Bb Bb ??

F1 X Bb Bb B b BB Bb bb F2 genotype – BB, Bb, Bb, bb F2 phenotype – 3 brown mice and one white mouse

F1 X Rr Rr F2 genotype – F2 phenotype –

Ratio In a cross where the 2 parents are true-breeding, the expected phenotype ratio in the F2 generation is: 3:1 Dominant Recessive

Build a baby Head: R= purple , r=yellow Body: B= blue, b=green Arms: A=orange , a =purple Legs: H=yellow, h=blue Eyes: E=pink , e=orange Nose: N = Green , n=yellow Mouth: P= pink p= purple

Build a baby What body colour is dominant, what letter is this represented by? Now take your baby and find it a partner. If they were to have babies of their own in the future, what colour of eyes might they have? Now do the same for body colour and arm colour.