Basic Genetic Concepts & Terms & Punnett Squares 1 Chapter Heredity and Genetics

Genetics: what is it? What is genetics? What is genetics?  “Genetics is the study of heredity, the process in which a parent passes certain genes onto their children.” What does that mean? What does that mean?  Children inherit their biological parents’ genes that express specific traits, such as some physical characteristics, natural talents, and genetic disorders. 2

Word Match Activity Match the genetic terms to their corresponding parts of the illustration. Match the genetic terms to their corresponding parts of the illustration. Handout Word Match WS base pair base pair cell cell chromosome chromosome DNA (Deoxyribonucleic Acid) DNA (Deoxyribonucleic Acid) *double helix*? *double helix*? genes genes nucleus nucleus 3

Word Match Activity base pair base pair cell cell chromosome chromosome DNA (Deoxyribonucleic Acid) DNA (Deoxyribonucleic Acid) double helix* double helix* genes genes nucleus nucleus Illustration Source: Talking Glossary of Genetic Terms y=chromosome y=chromosome y=chromosome 4 base pair cell nucleus chromosome (double helix) DNA genes

Genetic Concepts H describes how some traits are passed from parents to their children. H describes how some traits are passed from parents to their children. The traits are expressed by g, which are small sections of DNA that are coded for specific traits. The traits are expressed by g, which are small sections of DNA that are coded for specific traits. Genes are found on ch___. Genes are found on ch___. Humans have two sets of _ (hint: a number) chromosomes—one set from each parent. Humans have two sets of _ (hint: a number) chromosomes—one set from each parent. 5

Genetic Concepts Heredity describes how some traits are passed from parents to their children. Heredity describes how some traits are passed from parents to their children. The traits are expressed by genes, which are small sections of DNA that are coded for specific traits. The traits are expressed by genes, which are small sections of DNA that are coded for specific traits. Genes are found on chromosomes. Genes are found on chromosomes. Humans have two sets of 23 chromosomes— one set from each parent. Humans have two sets of 23 chromosomes— one set from each parent. 6

Genetic Terms – Allele: An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. genechromosomegenechromosome – Genes: It is a name given a part of DNA and RNA DNARNADNARNA – Dominant : The stronger of the two alleles. Expressed – Recessive: The weaker of the two alleles. Hidden – Homozygous: Both alleles are the same. – Heterozygous: Two different alleles. – Genotype: This is the "internally coded, inheritable information" carried by all living organisms. “Blueprint” – Phenotype: This is the "outward, physical manifestation" of the organism. – Mendellian Inheritance: A scientific theory of how hereditary characteristics are passed from parent organisms to their offspring. hereditary – Hybrid: A cross breeding of two purebreds. Red & White flowers. 7

Mendelian Inheritance 1. The inherited traits are determined by genes that are passed from parents to children. 2. A child inherits two sets of genes—one from each parent. 3. A trait may not be observable, but its gene can be passed to the next generation. 8

Mendelian Inheritance Each person has 2 copies of every gene—one copy from mom and a second copy from dad. These copies may come in different variations, known as alleles, that express different traits. Each person has 2 copies of every gene—one copy from mom and a second copy from dad. These copies may come in different variations, known as alleles, that express different traits. For example, 2 alleles in the gene for freckles are inherited from mom and dad:  allele from mom = has freckles (F) - Dominant  allele from dad = no freckles (f) - Recessive  child has the inherited gene pair of alleles, Ff (F allele from mom and f allele from dad). 9

Punnett Squares

What is a PUNNETT SQUARE? A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine A tool to predict the probability of certain traits in offspring that shows the different ways alleles can combine A way to show phenotype & genotype A way to show phenotype & genotype A chart that shows all the possible combinations of alleles that can result when genes are crossed A chart that shows all the possible combinations of alleles that can result when genes are crossed

What is a PUNNETT SQUARE? Letters stand for dominant and recessive alleles Letters stand for dominant and recessive alleles An uppercase letter stands for a dominant allele An uppercase letter stands for a dominant allele Lowercase letters stand for recessive alleles Lowercase letters stand for recessive alleles

Using a PUNNETT SQUARE To set up a Punnett square, draw a large square, and then divide it into 4 equal sections (also squares). It should look something like this:

Using a PUNNETT SQUARE Now you need two parents to mate, ones with a known genotype For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr For example, a red flower (genotype Rr) and a white flower (genotype rr). Rr x rr

Using a PUNNETT SQUARE Place one of the parents on top, and one on the left. You should get a something similar to this:

Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this:

Using a PUNNETT SQUARE The two-letter combinations are the possible genotypes of offspring The two-letter combinations are the possible genotypes of offspring They are: Rr, Rr, rr, and rr genotypes They are: Rr, Rr, rr, and rr genotypes From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%) From this it is possible to determine the probability (chance) that a flower will have a red phenotype (2/4 or 50%) or a white phenotype (2/4 or 50%)

Mendel’s Laws of Inheritance 1.Law of Dominance: In heterozygous genotypes, dominant alleles hide recessive alleles when both are inherited by an organism. (Hh means the dominant trait will show up in the phenotype)

Mendel’s Laws of Inheritance 1. The Law of Segregation (separation): Each organism has 2 alleles for a gene. Only one allele from each gene pair will be passed on to the offspring.

Homozygous/Heterozygous Cross a homozygous dominant tall plant with a homozygous recessive short plant. Cross a homozygous dominant tall plant with a homozygous recessive short plant. What letters would you use to represent this cross? Dominant trait = tall Dominant trait = tall Recessive trait = short Recessive trait = short T = tall T = tall t = short t = short Hmzg / Htzg

What is the genotype of a homozygous dominant tall plant? What is the genotype of a homozygous dominant tall plant? Genotype Genotype % TT % Tt % tt  TT TT x tt TT x tt What is the genotype of a homozygous recessive short plant? What is the genotype of a homozygous recessive short plant?  tt t t T TT T Phenotype Phenotype % tall % short Tt

2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit. o What letters would you use to represent this cross? Dominant trait = brown hair Dominant trait = brown hair Recessive trait = white hair Recessive trait = white hair B = brown B = brown b = white b = white

What is the genotype of a heterozygous brown haired rabbit? What is the genotype of a heterozygous brown haired rabbit? Genotype Genotype % BB % Bb % bb  Bb Bb x bb Bb x bb What is the genotype of a homozygous recessive white haired rabbit? What is the genotype of a homozygous recessive white haired rabbit?  bb b b BbBb Phenotype Phenotype % brown % white bb Bb 0 50

3.. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig. o What letters would you use to represent this cross? Dominant trait = long hair Dominant trait = long hair Recessive trait = short hair Recessive trait = short hair L = long L = long l = short l = short

What is the genotype of a homozygous dominant long haired guinea pig? What is the genotype of a homozygous dominant long haired guinea pig? Genotype Genotype % LL % Ll % ll  LL LL x Ll LL x Ll What is the genotype of a heterozygous long haired guinea pig? What is the genotype of a heterozygous long haired guinea pig?  Ll L l LL LL Phenotype Phenotype % long % short LLLl LLLl

4. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant.  What letters would you use to represent this cross? Dominant trait = wrinkly skin Dominant trait = wrinkly skin Recessive trait = smooth skin Recessive trait = smooth skin W = wrinkly W = wrinkly w = smooth w = smooth

What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant? Genotype Genotype % WW % Ww % ww  Ww Ww x Ww Ww x Ww What is the genotype of a heterozygous wrinkly-skinned elephant? What is the genotype of a heterozygous wrinkly-skinned elephant?  Ww W w WwWw Phenotype Phenotype % wrinkly % smooth Wwww WWWw

Phenotype Phenotype % round % wrinkled 5.A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have wrinkled seeds? RR x Rr RR x Rr R r RRRR RRRr RRRr R = round Genotype Genotype % RR % Rr % rr r = wrinkled