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Presentation on theme: "Heredity."— Presentation transcript:

1 Heredity

2 Heredity: the passing of genetic traits from parent to offspring
Characteristics: Hair Color Earlobes Fingers Traits: Type of hair color- brown, blonde, red Attached/unattached Longer index or ring finger A feature that has different forms in a population Different forms of a characteristic governed by genes

3 How traits are passed on….
Traits are determined by genes. Genes are the instruction manuals for our body. They provide directions for building all the proteins that make our bodies function. DNA is found within a gene. Genes are carried in chromosomes.

4 How traits are passed on…
Chromosomes are found in the nuclei of our cells. Everybody has 46 chromosomes (23 pairs)

5 How traits are passed on…
When a zygote (baby) is formed, it too has 46 chromosomes. It receives a copy of one of each of Mom’s chromosomes and a copy of each of Dad’s chromosomes for a total of 23 pairs of chromosomes. Not all living things have 23 pairs of chromosomes. our/

6 Genes are made up of two parts…
These parts are called alleles. An allele is one of the alternative forms of a gene that governs a characteristic. Alleles are represented by letters Capital letters represent dominant traits Lower case letter represent recessive traits A = dominant a = recessive

7 Traits are either dominant or recessive…
Dominant trait- the trait that always appears when a dominant allele is present in gene The trait observed in F1 when parents that have different traits are bred Recessive trait- the trait that does not appear unless there are 2 recessive alleles present in gene The trait that reappears in the F2 after disappearing in the F1 when parents with different traits are bred Ex) Brown hair is dominant over blonde hair, so if one brown allele is passed on from the parent the offspring will have brown hair Ex) In order for someone to have blonde hair both parents must have passed on a recessive gene, resulting in 2 recessive alleles

8 Traits and Inheritance
Phenotype: An organism’s appearance Detectable physical characteristics What an organism looks like Genotype: The entire genetic makeup of an organism the combination of genes for one or more specific traits Homozygous- 2 of the same type of allele (2 dominant or 2 recessive) Heterozygous- 2 different alleles, one dominant and one recessive (purebred) Ex. Yellow or green seed color Ex. For a recessive trait to show up the offspring must receive 2 recessive alleles, making it homozygous

9 Punnett Squares Used to organize all the possible combinations of offspring from particular parents

10 Gregor Mendel Born 1822 in Heinzendorf, Austria
Worked in Monastery garden Patterns of inheritance not always clear, sometimes a trait appeared in one generation (parents) and not in the next generation (F1, offspring), but then it reappears again in the generation after that (F2). Began investigating with pea plants Grow quickly self-pollination create true-breed parts of a flower cross-pollination

11 Mendel studied one characteristic at a time…
Characteristics Mendel's Experiments with peas

12 Genetic Instructions Mendel realized that each parent must have 2 “sets of instructions” for each trait When parents reproduced they each gave their offspring one set of each of their instructions (the child will then end up with 2 “sets of instructions” for each trait Mendel published his work in 1865 and not until 30 years later was his work rediscovered and understood A Gene is one set of instructions for an inherited trait An Allele is one of the alternative forms of a gene that governs a trait (ex. If earlobes are attached or unattached)

13 Punnett Squares Used to organize all the possible combinations of offspring from particular parents Cross of homozygous purple flower and homozygous white flower P = Purple (dominant) , p = white (recessive) Parent 1 Parent 2 Phenotype Purple white Genotype PP pp P P Pp F1 Generation: Genotype: Pp Phenotype: Purple p

14 Mendel’s 2nd Experiment
Like Mendel’s 2nd experiment, we will self pollinate the F1 generation Parent 1 Parent 2 Genotype Pp Phenotype Purple purple F2 Generation: Genotype: 1PP, 2Pp, 1pp Phenotype: 3purple, 1white Genotype Ratio: 1:2:1 Phenotype Ratio (dominant:recessive): 3:1 P p PP Pp pp P p

15 t t T t Tt Tt 2 Tt : 2 tt or 1:1 tt tt 2 Tt : 2 tt or 1:1

16 Incomplete dominance



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