All About DNA (cont.)

WHAT IS GENETICS? 

Genetics are the scientific study of heredity, which is the passing of traits from parents to offspring, such as hair color, eye color, or number of fingers or toes.

WHO WAS GREGOR MENDEL? 

Gregor Mendel was a monk who lived over 100 years in a monestary in Vienna, Italy, and he discovered the basic principles of heredity by breeding garden peas in carefully planned experiments. He was the first to develop rules that accurately predict patterns in heredity. In conducting his experiment, Mendell chose to study pea plants because they reproduce and grow quickly, so he could study many generations of pea plants within a short amount of time. Pea plants were the ideal plant to study for this type of experiment because they are considered very "simple" organsims since they express few genes. 

WHAT IS MENDELIAN GENETICS? 

(Vocab)

-Trait: heritable 

      •feature: petal color

-Allele: variant for a characteristic

       •purple (red and blue)

-P generation: parents

-F1 generation: first filial generation

The firs experiments Mendel conducted were monohybrid crosses, which involved one trait (flower color or seed shape). 

SO WHAT IS MENDEL'S THEORY

1) For each inherited trait, an individual has two copies, one from each parent (the traits come in pairs. This became the Law of Segregation, which means one trait from each parent.

2) There are alternative versions of traits. These become known as "alleles". 

3) When two different alleles occur together, one trait may be expressed while the other is not expressed.

4)Alleles for each trait separate independently when forming gametes (which are sex cells, such as eggs or sperm). Gametes only carry one allele for each trait. This became known as the Law of Independent Assortment, which means traits are inherited independently. 

DOMINANT V RECESSIVE 

A dominant trait is expressed if 1/2 of the alleles are present, while a recessive trait is expressed if two alleles are present.

HOMOZYGOUS V HETEROZYGOUS 

"Homozygous" means having a pair of identical alleles for a trait. (Think: "homo"=same) "Heterozygous" means hving two different alleles for a trait. 

WHAT IF THERE ARE EXTRA OR MISSING CHROMOSOMES? 

If humans are missing one chromosome, making 45 of the regular 46 chromosomes, the human usually does not survive. The mother's body will usually reject the embryo as it grows in her womb through the gestation period, resulting in a miscarriage. If the child is born, then they will usually pass away soon after birth. 

If there are extra copies of chromosomes, the result will be abnormal growth and disabilities or nondisfunction, which is when homologous chromosomes fail to separate. 

Mutations occur if there are changes in chromosomal structures (or the DNA codes). 

GENOTYPE V PHENOTYPE 

A genotype is the genetic make-up of an organism, and they are genes that are expeessed. A phenotype is the physical appearance of an organism; the result of genotypes. 

WHAT IS INCOMPLETE DOMINANCE? 

Incomplete dominance is a condition in which neither of the two traits in a pair masks the other, result in the blend of the traits. For example, if a blue and red flow had an offspring with incomplete dominance for petal color, the flower's color would be purple. In humans, the best known example of incomplete dominance are hazel eyes, which are the mixture (or separation) of light brown and extremely dark green. 

HOW DO CHROMOSOMES DETERMINE GENDER? 

There are things called autosomes, which are the 22 pairs of chromosomes that are not involved in determining a person's gender. The one chromosome that is involved in determining someone's gender is called the sex chromosome. Women have a matching set of X ( so XX) while men hav a set of XY (the Y makes the person of male gender). 

WHAT ARE SEX-LINKED TRAITS? 

Sex-linked traits are usually carried on the X chromosome, so, as a result, females are less likely than males to inherit sex-linked traits, such as color blindness, because they have a second countering X. Males are XY so if the sex-linked trait is carried on the X chromosome, then they woll either have the trait or not because they can only have one X chromosome.