# Growth week 8

version from 2018-01-14 18:55

## Section 1

Describe the relationship between genitalia development and pubic development in boysPubic hair development occurs late in pubertal development. But puberty occurs early with regard to peak height velocity. Diagonal relationship between pubic hair and genetalia development. 90% of of boys finished in terms of genitalia when they reach pubic hair five.
Describe the relationship between breast development and pubic development in girlssimilar relationship (as males) but shifted to the left. PHV is occuirng in B2/3/4. Menarche occurs in B3/4 after peak height velocity. Breast development is before PH development in girls.
What does G2 meanFirst appearance genitalia
The distributions of chronological age and skeletal age for boys at Tanner G2Equal variation in both chronological and skeletal age. Therefore in G2 you cannot predict from skeletal age what level of puberty they are in. Not critical.
The distributions of chronological age and skeletal age for girls at Tanner B2 Again an equivalent spread skeletal maturity and chronological age so again, skeletal maturity is not related to the initiation of pubertal development in girls.
Distributions of chronological age and skeletal age for boys at 95% mature heightIn this situation excludes all maturity is critical. For example for the boys in the sample all of them who had reached 95% mature height had a skeletal age between 14 and 15.999 years of age. Despite wider spread of chronological age. This
What does it mean if an aspect is critical It means that all of us should pass through that stage at the same time.
Distribution of chronological age as greater age for girls at 95% mature height 27 girls, mature height was reached between 11.5 and 14.5 years. And bar one girl, they all had skeletal maturity of between 12.5 and 13.5 years.
Correlations between SA and CA on reaching stages of developmentThe older you the more mature you in terms of skeletal development. More true for girls than boys. B2 correlation or girls = 0.69. G2 = 0.63.
CA, SA and menarche in girls. Regardless of CA, girls are at a similar SA at the age of menarche.

## Section 2

Turner's syndrome Missing an X chromosome (45XO). don't have normal gonads, have street gonads that don't produce estrogen and therefore they don't have AGS. Growth curve goes up to adulthood without AGS. 1/5000 people. Relatively common. Extremely short and don't show pubertal development- debilitating. Cant have children. Grow better with GH. Short stature; present with oedema at birth; low hair line; webbed neck. So many people in comparison to other growth disorders that a growth chart for turner syndrome girls was created.
Where does most of the information on the heritability of traits come from family studies and the resulting correlations between related and unrelated individuals.
Basic premise of heritability using family studiesIf the variation in a trait is largely under genetic control then related individuals will be more similar than unrelated individuals. ie. Intra-family variance < inter-family variance.
sigma squared =Variance
Equation for phenotypic variation = genetic variation + environmental variation. (sigma squared P = sigma squared G + sigma squared E) Sigma looks like O with little line on top O-
Heritability proportion of our inheritance that is due to genes opposed to phenotype. H^2 = Sigma squared G / sigma squared P.
PolygenicInheritance by a number of genes with difficult to determine small effects.
Oligogenicinheritance by few genes with pronounced and detectable effects.
Why does polygenic inheritance allow evolutionary advantage it allows more chance of adaptation and variation. more chance to survive and procreate.
Phenotypic, Genotypic and environmental correlations;The phenotypic correlation between two traits is a function of the h squared (heritability) of each trait (trait 1 and trait 2) and the genetic and environmental correlations between them. Varies from -1.0 to +1.0.
if h squared is low the phenotype is due to environmental factors
if h squared is high the phenotype is due to genetic factors.
Genotype x environment - effects on individuals not all children respond to the same degree to any given environmental factor. A portion of the different responses is due to genetic variation. e.g. thrifty genotype
Thrifty genotypeWhilst living in a food insecure environment, the genotype will be selected that provides protection against starvation. i.e. the genotype that favours the efficient storage of fat. In food abundant environments this ' thrify genotype' predisposes to obesity and type 2 diabetes. (Pima indians- 100% obesity and 65% NIDDM, have a genotype that preferentially stores fat). 42% of the US pima women obese and 35% men.
Genotype x sexsexual dimorphism in response to obesogenic environment. Males abdominal fat and female gluteofemoral fat.
Genotype x age timing of maturation. Genetically respond differently to the timing of endocrine release.

## Section 3

Study designs to examine genetics of growth family, twin, nuclear families, extended families/pedigrees, population studies.
Twin studiesMZ twins share 100% genotype. -phenotypic differences are environmental.
DZ twins share 50% genotype (like full siblings) phenotypic differences are genetic & environmental
*Common twin environments inflate h2
*Competition for maternal resources causes discordant foetal growth
Family studies1. 1st degree familial correlations - shared environments, secular trends. 2. Specific environmental factors e.g. diet not in analysis.
3. Mostly studies of (adult) height.
4. Cross-sectional.
5. Mostly magnitude of genetic effects rather than e.g. interaction studies.
Nuclear families- Correlations between 1st degree relatives
+Parent – offspring
+Sibling – sibling
+Spouse – spouse (100% environmental?)
*shared environment increases h2 e.g. diet, lifestyle
* Adjust h2 for spousal correlation
Extended families/pedigrees-Phenotypic correlations between all family members of varying degrees.
-Reduces shared environments e.g. same genes in different environments.
-Different environments for same genes allow G x E investigation
Population studies1. cannot suppose genetic differences because of phenotypic differences.
2. Environmental variation.
3. SES variation.
4. Climatic variation.
5. Nutritional variation.
Birthweight estimates of the influences of foetal genes, maternal genes, non-genetic maternal factors, environmental effects vary across studies because of unique foetal environment and interaction with mother
Skeletal dimensions tend to have high hirritability
Soft tissuestend to have low heritability
Maturation tends to have high heritability; dental emergence 0.85, skeletal maturity 0.45 and menarche 0.5
Birthweight of twins correlation 0.56
birthweight of sibs correlation 0.5
Height/weight correlation of MZ twins 0.9/0.8
Age of menarche of MZdifference of 2.8 months. amount of months increase as distance increases.