Grade 8 Science (K-12)- Mendelian Genetics and Non-Mendelian with simple illustrations and brief concept presentation

2. GREGOR MENDEL
-The Father of Genetics

3. Heredity
the biological process
whereby genetic factors are
transmitted from one
generation to the next.

4. Genes
the heritable units pass
on by parents to
offspring.

5. Traits- a distinguishing feature of your personal
nature.

6. Alleles
either of a pair (or series)of
genes that control the traits.

8. Dominant and Recessive Genes
• Gene that prevents the other gene from “showing” – Dominant
• Gene that does NOT “show” even though it is present – Recessive
• Symbol – Dominant gene – upper case letter – R
Recessive gene – lower case letter – r
Dominant
Color
Recessive
color

9. Results of crosses between
pure-breeding pea plants
Characters Studied Parents (F1) Generation
Seed Shape Round Wrinkled Round
Seed color Green Yellow Yellow
Seed coat color Colored White Colored
Pod Shape Inflated Constricted Inflated
Pod color Green Yellow Green
Flower position Axial Terminal Axial
Stem length Long Short Long

10. Mendel studies seven characteristics in the garden pea

11. Results of crosses between hybrid
plants
Characters Studied Hybrid F2 Generation Produced by Self-
Pollinating F1 Hybrids
Observed Ratio
Seed Shape Round Round Wrinkled 2.96: 1
Seed Color Yellow Green Yellow 3.01: 1
Seed Coat Color Colored Colored White 3. 15: 1
Pod Shape Inflated Inflated Constricted 2.95: 1
Pod Color Green Green Yellow 2.82: 1
Flower Position Axial Axial Terminal 3.14: 1
Stem Length Long Long Short 2.84: 1

12. Dominant and recessive traits of
garden pea
Characters Studied Dominant Trait Recessive Trait
Seed Shape Round Wrinkled
Seed color Green Yellow
Seed coat color Colored White
Pod Shape Inflated Constricted
Pod color Green Yellow
Flower position Axial Terminal
Stem length Long Short

13. :

14. Law of Dominance
In the monohybrid cross (mating of two organisms that differ in only one
character), one version disappeared.

15. Law of Segregation
during the formation of gametes (eggs or
sperm), the two alleles responsible for a trait
separate from each other.
alleles for a trait are then "recombined" at
fertilization, producing the genotype for the
traits of the offspring.

16. Applying the Law of Segregation
copyright cmassengale

18. gene combination for a
trait (e.g. RR, Rr, rr)
Genotype

19. the physical feature resulting
from a genotype (e.g. red,
white)
Phenotype

20. Genotype & Phenotype in Flowers
Genotype of alleles:
R = red flower
r = yellow flower
All genes occur in pairs, so 2
alleles affect a characteristic
Possible combinations are:
Genotypes RR Rr rr
Phenotypes RED RED YELLOW

21. Genotypes Combination
 Homozygous genotype - gene combination
involving 2 dominant or 2 recessive genes (e.g.
RR or rr); also called pure
 Heterozygous genotype - gene combination
of one dominant & one recessive allele (e.g.
Rr); also called hybrid
copyright cmassengale

22. RR
R R rr
rr
Round Wrinkled
Gametes Gametes

23. Self-fertilization Technique
When self-fertilized, homozygotes always
produce pure-breeding plants. When you
mixed round-seeded peas to another
round-seeded peas the offspring will be
only round-seeded peas.

24. Testcross Technique
involves a cross between the recessive
parental type.

25. Punnett Square

26. Types of Genetic Crosses
Monohybrid cross - cross involving a
single trait. ex. flower color
Dihybrid cross - cross involving two
traits. ex. flower color & plant height

27. The Law of Independent Assortment
Mendel derived the law of segregation by
following a single character
The F1 offspring produced in this cross were
monohybrids, individuals that are
heterozygous for one character
A cross between such heterozygotes is called a
monohybrid cross

29. Incomplete Dominance
Also known as “blending” b/c neither allele in a
pair is fully expressed
Example seen in Shorthorn Cattle
C = color gene with
alleles possible = CR (red), CW (white)
Cross a red bull with a white cow (Punnett
Square)

30. Incomplete dominance and
• When one allele is NOT completely dominant over
another (they blend) – incomplete dominance
Example: In carnations the color red (R) is incompletely
dominant over white (W). The hybrid color is
pink. Give the genotypic and phenotypic ratio from a
cross between 2 pink flowers.
RW X RW
RR RW
RW WW
R
WR
W
Genotypic = 1 RR : 2 RW : 1 WW
Phenotypic = 1 red : 2 pink : 1 white

31. • When both alleles are expressed – Codominance
Example: In certain chickens black feathers are codominant with
white feathers.
Heterozygous chickens have black and white speckled feathers.
Codominance

32. Multiple Alleles
Sometimes a trait is coded for by more than
just two alleles
Example = human blood type has 3 alleles
A, B, or O

33. Sex-influenced Traits
Aka, “Gender-influenced”
Usually influenced by sex hormones like
estrogen, testosterone
Examples: include baldness, Red-Green
colorblindness, Hemophilia

34. Hemophilia Colorblindness